Two fair dice; observe the sum
Repeat till the sum is prime or a perfect square
Given: the stop is a perfect square before a prime
p=P(odd square∣square before prime)
To find: 14p
Sums: 2,3,4,5,6,7,8,9,10,11,12
Primes: 2,3,5,7,11
Perfect squares: 4, 9
Prime sums: 2:1, 3:2, 5:4, 7:6, 11:2
Total=1+2+4+6+2=15
P(prime)=3615
Square sums: 4:3, 9:4⇒3+4=7
P(square)=367
Others (repeat): 6:5, 8:5, 10:3, 12:1
P(repeat)=3614
Re-rolls are irrelevant⇒race is prime vs square
P(square before prime)=7/36+15/367/36=227
Given a square: 4→3 ways,9→4 ways
Odd square=9 only
p=3+44=74
14p=14×74=8