Ihave three feet but can't walk; i tell you things but can't talk; sometimes i bend but i'm mostly straight. i'm like a scale but can't tell your weight. what am i?

Abox 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)