Probability (1 Viewer)

[cutemouse]

In group A there are 7 boys and 3 girls
In group B there are 2 boys and 8 girls

If two people are selected at random from either of group A and B, find the probability that both are boys.

Answer is 11/45... I keep getting 22/45

Thanks

 

[Pwnage101]

Required Probability

= P(group A is selected AND both chosen people are boys) + P(group A is selected AND both chosen people are boys)

=P(group A is selected )P(both chosen people are boys, given group A is selected) + P(group B is selected )P(both chosen people are boys, given group B is selected)

=0.5*[(7/10)*(6/9)]+0.5*[(2/10)*(1/9)] ---> Assuimg choosing from group A or group B is equally likely.

{Alternatively, = 0.5*[(7C2)/(10C2)]+0.5*[(2C2)/(10C2)]}

=7/30 + 1/90

=11/45

 

[cutemouse]

Hi,

Also could you find the prob if, one is a boy and one a girl?

Thanks

 

[Pwnage101]

I've provided a {very solid} solution to the initial problem; to find the probability you are now asking for, you need only amend my method in particular parts.

Have a go yourself ...

 

[cutemouse]

I did... and I can't get the answer (which is 37/90).

I get 7/20 :S

EDIT: I got the answer. Stupid calculator error -_-; Thanks alot!