Question

In a box someone has accidently mixed 5V, 10V and 15V relays. The box contains 100 relays: 60 are 5V, 25 are 10V, and 15 are 15V. Three relays will be drawn out one at a time checked and then put back. Match the probabilities.

Answer 1

Total Number of Relays = 100

Number of 5V relays = 60

Number of 10V relays = 25

Number of 15V relays = 15

Probabilities:

All the drawn are 5V relays = 60 / 100 = 0.6

All the drawn are 10V relays = 25 / 100 = 0.25

All the drawn are 15V relays = 15 / 100 = 0.15

At least one is 10V relays = (60 / 100) x (59/99) + (25/100) x (25/99) + (15/100)(15/99)= 0.35758 + 0.06313 + 0.02273 = 0.44344 = 0.44