Help with probability !!

Neewbie_noob · 06-09-2012 04:12PM #1

Can someone help me work out the probability if there was a drum with 50 numbers and I have to guess the 5 numbers that will come out. What is the probability of me getting it right ?? ( Like a lotto ).

ALSO

What is the probability of there being a drum with 50 numbers, I have to guess correctly 3 of the 5 numbers drawn (like in Paddy Powers).

I think I have the first one correct, but correct me if I'm wrong. To get the 5 numbers out of 50 (in no particular order, like in Lotto).

50*49*48*47*46 254251200

=

= 2118760
5! 120

Thanks for your help everyone, and sorry mods if this is in the wrong forum

Monotype · 06-09-2012 04:21PM

There's a formula for that - 50C5.

where nCr = n!/(n-r)!r!

- which is the same value as what you got. You can find that on any (good) scientific calculator.

Neewbie_noob · 06-09-2012 04:22PM

Monotype wrote: »

There's a formula for that - 50C5.

where nCr = n!/(n-r)!r!

- which is the same value as what you got.

Then for guessing only 3 of the numbers drawn out of the 5 is it 50C5C3 ??

Monotype · 06-09-2012 04:41PM

I think you have to consider how many different groups with 3 that you get in it.

So say if your winning numbers were 24, 25, 31, 32, 35.
You could win with {24, 25, 31} or {24, 31, 32} or {24, 31, 35}...
So you need to select 3 numbers from 5.
5C3 = 10
So we have 10 sets that can have winning numbers.

Now you'll be choosing 5 numbers yourself, not 3. So each of those extra sets have got an extra 2 numbers tacked on.
How many sets can you have then? Bear in mind that these numbers can't be any of the winning numbers.
In other words... how many combinations for the 4th and 5th number are there?

ray giraffe · 09-09-2012 03:49AM

Neewbie_noob wrote: »

Then for guessing only 3 of the numbers drawn out of the 5 is it 50C5C3 ??

Solution to similar problem here!

Also check out http://en.wikipedia.org/wiki/Lottery_mathematics

Help with probability !!

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