Question

Find the probability that a number from 1 to 300 is divisible by 3 or 7 ?

Answer 1

Between 1 to 300:
   the numbers divisible by 3:  3*1, 3*2, .... 3*100
   the numbers divisible by 7:  7*1, 7*2,.... 7* 42
   the numbers divisible by both: 21*1, 21*2,...  21*14

Number of  integers divisible by 3 or 7 :  total:  100 + 42 - 14 = 128

Probability = 128 / 300 = 32 / 75