Q:- Three horses A B and C are in race. A is twice as likely to win as B and B is twice as likely to win as C.what is the probability that B or C wins.

The total probability is 1.

So, P(A)+P(B)+P(C)=1
Since P(A) = 2P(B) and P(B)=2P(C), you can rewrite

P(A)+P(B)+P(C)=1 as 2P(B)+P(B)+0.5P(B)=1

Therefore P(B) = 1/(2+1+0.5) = 1/3.5 = 2/7

For P(C), it'll be 4P(C)+2P(C)+P(C) = 1

And P(C) = 1/(4+2+1) = 1/7

P(B or C) = 1/7 + 2/7 = 3/7

Ok? :)