Hi Probability experts..... Can you solve this problem.

[NualaJ]

Hi lads,

I'm looking to solve this probability problem. Nobody i've given it to has solved it yet, and I'm a maths teacher, and I can't solve it. So I'm putting it to you to see if it's solvable at all!! It's from Leaving Cert Exam 2011.

There are 16 girls and 8 boys in a class.
Half of these 24 students study French.
The probability that a randomly selected girl studies French is 1.5 times the probability that a randomly selected boy studies French.
How many of the boys in the class study French?

Hope ye can help :-)

[lancearmstrong1313]

I believe 3 boys and 9 girls study French.

Boys & French = 3
Boys & ~French = 5

Girls & French = 9
Girls & ~French = 7

You are looking for the P(French | Girl) = 1.5*P(French | Boy)

Currently, the P(French | Girl) = 9/16
and the P(French | Boy) = 3/8

So (9/16)/(3/8) = 1.5.

I think that should solve it for you

[NualaJ]

Thank You that was very helpful