Question

A box contains 40 number tiles numbered 1 to 40. If a tile is drawn at random, what is the probability that the number drawn is a multiple of 3 or 4? Find P(Multiple of 4 or Multiple of 5)

Answer 1

Multiples of 3 are 3, 6, 9, ... 39, or 3*1, 3*2, ,,,3*13, so there are 13 of them.

Multiples of 4 are 4*1 pto 4*10, or 10 of them

Multiples of both 3 and 4 are 3*4*1 to 3*4*3,

or 12, 24, 36, 3 of them.

Multiples of either 3 or 4 are 3, 4, 6, 8, ..., 40,

13+10-3 = 20 of them.

P(multiple of either 3 or 4) = 20/40 = 0.5

P(multiple of 4 or 5) = (10+8-2)/40 = 16/40 = 0.4

Explanation: