Question

Tiles numbered 1 through 25 are placed in a box. Tiles numbered 11 through 30 are placed in a second box. The first tile is randomly drawn from the first box. The second tile is randomly drawn from the second box. Find each probability.

The first tile is a multiple of 3 or prime and the second tile is a multiple of 5.

Answer 1

The first tile is a multiple of 3 or prime
there are 8 multiples of 3 from 1-25
there are 9 primes from 1-25 (2, 3, 5, 7, 11, 13, 17, 19, 23)
8+9=17, but subtract 1 because 3 was counted twice --> P=16/25=0.64
The 2nd tile is a multiple of 5
There are 4 multiples of 5 from 11-30 (15, 20, 25, 30) --> P=4/20=0.2