Lame ass maths riddle

nyarlothothep · 20-04-2011 11:21pm #1

What is 30÷2(2+3)÷5

Is it 15?

or 0.6?
...
Or is this question broken?

hondasam · 21-04-2011 12:07am

I Don't understand the question

nyarlothothep · 21-04-2011 1:27am

Well what does the equation equal? Or is there something wrong with it?

21-04-2011 1:36am

Isn't it 15?

30 divided by two

equals 15

2 plus three equals 5

15 multiplied by five equals 75

75 divided by five is fifteen.

No? It's been a while since I was in school, but I thought that was the way it worked

Cavehill Red · 21-04-2011 1:43am

It's 30 over the 2(2+3) over 5.
So that's 30 divided by (2X5) divided by 5.
Which is 30/10 divided by 5.
Which is 3/5 = 0.6.

JBnaglfar · 21-04-2011 1:34pm

^^ I got that at first.

If you want to get 15 you can.

2(2+3) divided by 5 = 2
30 divided by 2 = 15.

This is basically asking 30 divided by 10 divided by 5, and I didn't think maths necessarily went from left to right.

Edit: google suggests .6 is correct
link

nyarlothothep · 21-04-2011 3:01pm

I love troll maths

mari2222 · 21-04-2011 3:06pm

it is 15. to get the answer .6 you would need another set of brackets within the equation.

nyarlothothep · 21-04-2011 3:08pm

Here's another one

-20=-20
16-36=25-45 (16-36=-20,25-45=-20)
4^2-36 = 5^2-45 (4^2=16,5^2=25)
4^2-36 = 5^2-45
4^2-2.4.9/2 = 5^2-2.5.9/2 (2.4.9/2=36,2.5.9/2=45)
4^2-2.4.9/2 +(9/2)^2 = 5^2-2.5.9/2 +(9/2)^2 (adding both the sides (9/2)^2
[4-(9/2)]^2 = [5-(9/2)]^2 (let 4=a,9/2=b)
4-(9/2) = 5-(9/2)
4 = 5
2+2 = 5

And

10x^2-19x=-6 =?

2cool4school · 21-04-2011 3:10pm

youve lost me lads

stimpson · 21-04-2011 3:13pm

http://lmgtfy.com/?q=30%C3%B72(2%2B3)%C3%B75

desertstorm · 21-04-2011 3:30pm

MoodeRator · 21-04-2011 3:33pm

nyarlothothep wrote: »

What is 30÷2(2+3)÷5

Is it 15?

or 0.6?
...
Or is this question broken?

30÷2(2+3)÷5
15(5)/5
=15

Maybe or maybe not. But I read it exactly the same as Papa smut

21-04-2011 3:34pm

0.6 - brackets first, then multiplication, then divide left->right

A common technique for remembering the order of operations is the abbreviation "PEMDAS", which is turned into the phrase "Please Excuse My Dear Aunt Sally". It stands for "Parentheses, Exponents, Multiplication and Division, and Addition and Subtraction".

http://www.purplemath.com/modules/orderops.htm

MoodeRator · 21-04-2011 3:37pm

bluewolf wrote: »

0.6 - brackets first, then multiplication, then divide left->right

http://www.purplemath.com/modules/orderops.htm

I'll just put my hat back on and go stand in my corner again.

Cool Mo D · 21-04-2011 3:38pm

It's only a riddle if you can't remember primary school maths. Brackets first, then multiplication, then division. There is more than one division, then go left to right, giving 0.6.

MJRS · 06-05-2011 9:45pm

I thought multiplication and division were equal priority so you just do left to right? Hence the acronym being BOMDAS or BODMAS, both are valid. Isn't this one of loads of maths problems with two provable correct answers?

Got this from the ever reliable wiki "These mnemonics may be misleading,
especially if the user is not aware that
multiplication and division are of equal
precedence, as are addition and subtraction."

Saila · 08-05-2011 9:07am

answer = 0.6

onlyrocknroll · 08-05-2011 9:22am

0.6

Didn't your teacher teach you about BOMDAS?

edit; oops missed MJRS's post

MARTINOZ · 11-05-2011 7:31am

Anyone that got 0.6 needs to go back to primary school.

http://www.google.com.au/search?hl=en&source=hp&biw=1004&bih=610&q=30%2F2%282%2B3%29%2F5+%3D&oq=30%2F2%282%2B3%29%2F5+%3D&aq=f&aqi=&aql=f&gs_sm=e&gs_upl=1391l34015l0l17l17l2l6l0l0l453l2328l2-6.0.2

randombar · 13-05-2011 10:26am

Back in my day it was BOMDAS!!

davetherave · 13-05-2011 10:34am

2cool4school wrote: »

youve lost me lads

Maybe you should have stayed in school??

....sorry

It's 0.6.

30÷2(2+3)÷5 brackets first
30÷2(5)÷5 then multiplication
30÷10÷5 then division left to right
3÷5
0.6

13-05-2011 10:49am

It's 15. The only way it could be 0.6 is if you redefine 5(2+3) to mean (5 * (2+3)) instead of 5 * (2+3). Bracket notation for multiplication is just shorthand, it doesn't change the precedence.

30÷2(2+3)÷5
= 30÷2(5)÷5
= 30÷2*5÷5 (÷ and * have equal precedence and are left-associative, so you do them left-to-right)
= 15*5÷5
= 75÷5
= 15

The bolded part is where most people make their mistake. "Brackets first" means you calculate what is inside the brackets first. when brackets are used for multiplication it is just shorthand for *.

onlyrocknroll · 13-05-2011 11:15am

28064212 wrote: »

It's 15. The only way it could be 0.6 is if you redefine 5(2+3) to mean (5 * (2+3)) instead of 5 * (2+3). Bracket notation for multiplication is just shorthand, it doesn't change the precedence.

30÷2(2+3)÷5
= 30÷2(5)÷5
= 30÷2*5÷5 (÷ and * have equal precedence and are left-associative, so you do them left-to-right)
= 15*5÷5
= 75÷5
= 15

The bolded part is where most people make their mistake. "Brackets first" means you calculate what is inside the brackets first. when brackets are used for multiplication it is just shorthand for *.

Damn you, I thought I was right and now I'm confused.

Why have you forsaken me BOMDAS?

im invisible · 19-05-2011 5:18pm

i dont know, maybe ask in the maths forum?

Mellor · 24-05-2011 8:16am

JBnaglfar wrote: »

^^ I got that at first.

If you want to get 15 you can.

2(2+3) divided by 5 = 2
30 divided by 2 = 15.

This is basically asking 30 divided by 10 divided by 5, and I didn't think maths necessarily went from left to right.

Edit: google suggests .6 is correct
link

no it doesn't

http://www.google.ie/search?rlz=1C1DVCP_enIE394IE394&sourceid=chrome&ie=UTF-8&q=30+divided+by+10+divided+by+5#sclient=psy&hl=en&rlz=1C1DVCP_enIE394IE394&source=hp&q=30%C3%B72(2%2B3)%C3%B75&aq=&aqi=&aql=&oq=&pbx=1&bav=on.2,or.r_gc.r_pw.&fp=9838aa61b26af9a1&biw=1312&bih=560

Cool Mo D wrote: »

It's only a riddle if you can't remember primary school maths. Brackets first, then multiplication, then division. There is more than one division, then go left to right, giving 0.6.

davetherave wrote: »

Maybe you should have stayed in school?? ....sorry
It's 0.6.

30÷2(2+3)÷5 brackets first
30÷2(5)÷5 then multiplication
30÷10÷5 then division left to right
3÷5
0.6

LMFAO

Trying to be condesending and end up looking like a fool
You should probably go back to school your self guys

30÷2(2+3)÷5............so brackets first
30÷2(5)÷5................2(5) is a shorthand way of writing 2x5, so lets change that so you don't get confused
30÷2x5÷5..................Multiplication and division arecomplimentary so the order doesn't matter

30x5÷5÷2
30÷5÷2x5 etc all equal 15

Anybody that is getting .6 is obviously dividing 30 by 10
That's the same as dividing by both 2 and 5. Which is obviously wrong as their is no ÷ before the 5.
For that to be the case it would have to read

30÷(2(2+3))÷5 or 30÷2÷(2+3)÷5

martineatworld · 24-05-2011 8:39am

I don't know why anyone is being condescending tbh.

According to Mellor's link, Google is putting in an extra pair of brackets to come up with that answer. There's an ambiguity about the structure of the question that leads me to believe that both answers are valid

Which leads to petty squabbles on the internet about who's right given there are two valid ways.

24-05-2011 8:45am

martineatworld wrote: »

I don't know why anyone is being condescending tbh.

According to Mellor's link, Google is putting in an extra pair of brackets to come up with that answer. There's an ambiguity about the structure of the question that leads me to believe that both answers are valid

Which leads to petty squabbles on the internet about who's right given there are two valid ways.

Google puts in brackets for clarification, it doesn't change the precedence. Put in 6 - 2 * 3 and it will "change" it to 6 - (2 * 3).

The only way there's ambiguity is if you change 2(5) to mean something different to 2 * 5

Mellor · 24-05-2011 8:54am

There is only something ambiguous if you make a mistake

ClutchIt · 24-05-2011 8:57am

The question is broken really. Even though there is a correct way of doing it, anyone who writes an equation in that fashion is an ignoramus

GT_TDI_150 · 24-05-2011 9:11am

nyarlothothep wrote: »

What is 30÷2(2+3)÷5

Is it 15?

or 0.6?
...
Or is this question broken?

just saw this,

I thought you first caclulate whats in the brackets -> (2+3) = 5
then you multiply it by 2 -> 2(5)=10
then the 2 divisions are dont in the order they appear sp first 30/10=3
then 3/5=.6

could be well wrong

24-05-2011 9:12am

Dublin_Gunner wrote: »

Work from left to right, breaking the equation into sections (and using BOMDAS as your guide).

The answer is 0.6

Only if you ignore precedence and associativity rules. You do not multiply 2(5) before dividing 30 by 2. The "B" in BOMDAS only refers to operations inside brackets. 2(5) is just shorthand for 2 * 5, and 30 ÷ 2 * 5 ÷ 5 is 15

RHunce · 25-05-2011 1:12am

MJRS wrote: »

I thought multiplication and division were equal priority so you just do left to right? Hence the acronym being BOMDAS or BODMAS, both are valid. Isn't this one of loads of maths problems with two provable correct answers?

Got this from the ever reliable wiki "These mnemonics may be misleading,
especially if the user is not aware that
multiplication and division are of equal
precedence, as are addition and subtraction."

What about BIRDMAS brackets, indices, roots, division, multiplication, addition and subtraction? Same answer anyway

nyarlothothep wrote: »

What is

Is it 15?

or 0.6?
...
Or is this question broken?

30÷2(2+3)÷5

30÷(2)(5)÷5

(30÷10)÷5

3÷5 = .6

Kadongy · 25-05-2011 1:32am

desertstorm wrote: »

This is true for a pixel representation of a circle (but not for an actual circle of course).

Mellor · 25-05-2011 7:22am

ClutchIt wrote: »

The question is broken really. Even though there is a correct way of doing it, anyone who writes an equation in that fashion is an ignoramus

nobody would write an quetion that way, the whole purpose of writing it that way is to confuse people with a weak understanding

RHunce wrote: »

What about BIRDMAS brackets, indices, roots, division, multiplication, addition and subtraction? Same answer anyway

30÷(2)(5)÷5

(30÷10)÷5

You realise that you can't get from to (30÷10)÷5
You just applied the division sign to the first 5, which is retarded.
You can't multiply 2 inside the brackets when there is a ÷ sign before it. Only + or -

30÷(2)(5)÷5
15(5)÷5

I imagine you can finish from there:rolleyes:

RHunce · 25-05-2011 12:41pm

Mellor wrote: »

You realise that you can't get from to (30÷10)÷5
You just applied the division sign to the first 5, which is retarded.
You can't multiply 2 inside the brackets when there is a ÷ sign before it. Only + or -

30÷(2)(5)÷5
15(5)÷5

I imagine you can finish from there:rolleyes:

My B2 in Honours Maths says otherwise :pac:

25-05-2011 12:43pm

RHunce wrote: »

30÷2(2+3)÷5

30÷(2)(5)÷5

(30÷10)÷5

3÷5 = .6

Why are you multiplying (2)(5) first? How is 30÷(2)(5)÷5 any different to 30÷2*5÷5?

Again, brackets precedence only applies to operations inside the brackets

Triangla · 25-05-2011 12:49pm

Typed equation exactly as typed into my scientific calculator, answer is 0.6.

ManFromAtlantis · 25-05-2011 12:55pm

RHunce wrote: »

My B2 in Honours Maths says otherwise :pac:

what would a B2 be worth when maths was maths in the 70's or 80's ?

RHunce · 25-05-2011 8:17pm

Still maths pal, I'm not doing that project maths ****e, don't be bitter because you did OL

onlyrocknroll · 25-05-2011 8:38pm

Wow the standard of this debate has really nosedived.

26-05-2011 1:42am

RHunce wrote: »

Still maths pal, I'm not doing that project maths ****e, don't be bitter because you did OL

But you're wrong. The answer is 15. Go back and read the thread

Mellor · 26-05-2011 7:49am

RHunce wrote: »

My B2 in Honours Maths says otherwise :pac:

LMFAO

Maybe if you knew what you were doing you would of goten an A2, like i did :cool:

Triangla wrote: »

Typed equation exactly as typed into my scientific calculator, answer is 0.6.

I'm not going to be so silly as to say the calculator is wrong, but I guarantee you that you typed it in wrong.
It's a well know problem, its exists in many forms.

onlyrocknroll · 26-05-2011 9:42am

Mellor wrote: »

LMFAO

Maybe if you knew what you were doing you would of goten an A2, like i did :cool:

I'm not going to be so silly as to say the calculator is wrong, but I guarantee you that you typed it in wrong.
It's a well know problem, its exists in many forms.

Mellor can you please post a link that explains why your way is correct and the other is wrong. I was sure it was 15 at first until I was convinced otherwise, now it's annoying me.

26-05-2011 9:46am

onlyrocknroll wrote: »

Mellor can you please post a link that explains why your way is correct and the other is wrong. I was sure it was 15 at first until I was convinced otherwise, now it's annoying me.

What parts of these posts don't you understand?

28064212 wrote: »

It's 15. The only way it could be 0.6 is if you redefine 5(2+3) to mean (5 * (2+3)) instead of 5 * (2+3). Bracket notation for multiplication is just shorthand, it doesn't change the precedence.

30÷2(2+3)÷5
= 30÷2(5)÷5
= 30÷2*5÷5 (÷ and * have equal precedence and are left-associative, so you do them left-to-right)
= 15*5÷5
= 75÷5
= 15

The bolded part is where most people make their mistake. "Brackets first" means you calculate what is inside the brackets first. when brackets are used for multiplication it is just shorthand for *.

28064212 wrote: »

Google puts in brackets for clarification, it doesn't change the precedence. Put in 6 - 2 * 3 and it will "change" it to 6 - (2 * 3).

The only way there's ambiguity is if you change 2(5) to mean something different to 2 * 5

28064212 wrote: »

Only if you ignore precedence and associativity rules. You do not multiply 2(5) before dividing 30 by 2. The "B" in BOMDAS only refers to operations inside brackets. 2(5) is just shorthand for 2 * 5, and 30 ÷ 2 * 5 ÷ 5 is 15

28064212 wrote: »

Why are you multiplying (2)(5) first? How is 30÷(2)(5)÷5 any different to 30÷2*5÷5?

Again, brackets precedence only applies to operations inside the brackets

Triangla · 26-05-2011 10:34am

http://i1193.photobucket.com/albums/aa345/myggel2011/IMAG0605.jpg

onlyrocknroll · 26-05-2011 11:29am

28064212 wrote: »

What parts of these posts don't you understand?

I understand all these posts. However they are just people stated what rules they followed, rather than providing any evidence that these are the correct rules.

Can you direct me somewhere where I can read an explanation of how to solve this correctly please.

26-05-2011 11:36am

onlyrocknroll wrote: »

I understand all these posts. However they are just people stated what rules they followed, rather than providing any evidence that these are the correct rules.

Can you direct me somewhere where I can read an explanation of how to solve this correctly please.

Order of operations => Do what's inside the brackets first. All the other operations are of equal precedence (multiplication and division), so we look at...
Operator associativity => multiplication and division are both left-associative, so are performed from left-to-right

Mellor · 27-05-2011 7:38am

onlyrocknroll wrote: »

I understand all these posts. However they are just people stated what rules they followed, rather than providing any evidence that these are the correct rules.

Can you direct me somewhere where I can read an explanation of how to solve this correctly please.

But anybody getting 0.6 isn't following the rules, they are bringing ÷2 inside the brackets. nowhere rules has been posted that allows that.

30÷2(2+3)÷5 so we all agree that ÷5 is at the end and the 2+3 = 5, so this is the part that is confsuing people

30÷2(5)

What people are doing is multiplying ÷2 by 5 and getting ÷10 which is wrong. If it said ÷(2(5)) it wouls be fine but it doesn't, the ÷ sign is fixed to the 2

÷2(5) = ÷2x5 = x5÷2 = x2.5

or

÷2 is the same as x(1/2) or x(.5), (.5)x(5)= x2.5

Triangla - That's interesting.
A google search suggests thats it not unheards of, casio calculators gettign confused. Apparently it's due to a built in coding to solve multiplication implied by brackets first. a rule that doesn't exist (its just the way people write) unless you believe 2(5) is different to 2x5,
I imagine if you put a x sign before the bracket it returns 15. I hope we all agree that there is no difference.

Mellor · 27-05-2011 7:43am

Another one I've seen is

6÷2(1+2)

Again, you can see the same structure. The brackets draw you attention to the right, where you end up with 6÷2(3) and get 1

But it's wrong. 6÷2(3) is just shorthand. It should be re-written as 6÷2x3

It's written in a confusing way on purpose. It should never have been like that to begin with

magicianz · 27-05-2011 7:58am

Its clearly 8.1.....

Thirty \ 4 + 3 \ 5

7.5 + .6

8.1 simples

Lame ass maths riddle

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