A number is chosen randomly from the numbers 1-20. If event A = {a multiple of 5}, what is the value of P(A')?

Question

1. A number is chosen randomly from the numbers 1-20. If event A = {a multiple of 5}, what is the value of P(A')?

Would it be 17/20? I did: Multiples of 5 between 1-20 (5,10,15) 3 numbers, 3/20, P(A) + P(A') = 1 P(A') = 1 - P(A) = 1 - 3/20 = 17/20

Answer 1

No. There are 4 multiples of 5 between 1 and 20 (5. 10, 15, 20)

so p(A) = 4/20

p(A') = 1 - (4/20) = 16/20 = 4/5