Question

You have cards numbered 1-10 and a number cube what are the odds of getting two prime numbers? The book says 1\5 but how do they get it.

Answer 1

I assume you pick a card, then throw the die

primes from 1-10 : 2,3,5,7 , so 4 of them
primes on a die: 2 3 5, so 3 of them
prob(2 primes) = (4/10)(3/6) = 1/5
prob(not 2 primes) = 4/5

odds in favour of getting two primes = (1/5) : (4/5
= 1 : 4