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# Lame ass maths riddle

• 20-04-2011 11:21pm
Registered Users, Registered Users 2 Posts: 5,177 ✭✭✭

What is 30÷2(2+3)÷5

Is it 15?

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

«13

• Closed Accounts Posts: 34,418 ✭✭✭✭

I Don't understand the question

• Registered Users, Registered Users 2 Posts: 5,177 ✭✭✭

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

• Posts: 0

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

• Registered Users, Registered Users 2 Posts: 6,109 ✭✭✭

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.

• Registered Users, Registered Users 2 Posts: 841 ✭✭✭

^^ 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

• Registered Users, Registered Users 2 Posts: 5,177 ✭✭✭

I love troll maths

• Registered Users, Registered Users 2 Posts: 568 ✭✭✭

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

• Registered Users, Registered Users 2 Posts: 5,177 ✭✭✭

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 =?

• Closed Accounts Posts: 162 ✭✭

• Registered Users, Registered Users 2 Posts: 7,821 ✭✭✭

• Registered Users, Registered Users 2 Posts: 373 ✭✭

• Registered Users, Registered Users 2 Posts: 1,726 ✭✭✭

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

• Posts: 0 CMod ✭✭✭✭

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

• Registered Users, Registered Users 2 Posts: 1,726 ✭✭✭

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.

• Registered Users, Registered Users 2 Posts: 1,419 ✭✭✭

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.

• Registered Users Posts: 331 ✭✭

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."

• Closed Accounts Posts: 7,751 ✭✭✭

• Registered Users Posts: 750 ✭✭✭

0.6

edit; oops missed MJRS's post

• Registered Users, Registered Users 2 Posts: 3,409 ✭✭✭

Back in my day it was BOMDAS!!

• Registered Users, Registered Users 2 Posts: 3,435 ✭✭✭

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

• Registered Users, Registered Users 2 Posts: 10,790 ✭✭✭✭

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 *.

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• Registered Users Posts: 750 ✭✭✭

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?

• Closed Accounts Posts: 4,372 ✭✭✭

i dont know, maybe ask in the maths forum?

• Registered Users, Registered Users 2 Posts: 39,576 ✭✭✭✭

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
no it doesn't

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.
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

• Registered Users, Registered Users 2 Posts: 1,139 ✭✭✭

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.

• Registered Users, Registered Users 2 Posts: 10,790 ✭✭✭✭

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

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• Registered Users, Registered Users 2 Posts: 39,576 ✭✭✭✭

There is only something ambiguous if you make a mistake

• Registered Users, Registered Users 2 Posts: 709 ✭✭✭

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

• Registered Users, Registered Users 2 Posts: 10,917 ✭✭✭✭

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