Question 259715
probability that they play is 9 times the probability that they don't.


let p(y) = probability that they play.


let p(n) = probability that they don't play.


p(y) = 9 * p(n)


the probability that they play plus the probability that they don't play must equal 1 since these options are mutually exclusive and there are no other options.


you get:


p(y) + p(n) = 1


now:

p(y) = 9 * p(n), so this equation is equivalent to:


9*p(n) + p(n) = 1


this means that 10*p(n) = 1


this means that p(n) = 1/10 = .1


this means that p(y) = 9 * p(n) = 9 * .1 = .9


p(y) = .9
p(n) = .1


the probability that san francisco plays in the next super bowl is .9 * 100% = 90%.