40 Day and 40 Nights
If it rains for 40 days and 40 nights, and dumps enough water over the face of the earth to cover the highest mountains (the Himalayas), how fast is it raining? (We won't worry about where all that water would come from.)

Answer:

6 inches per minute

Calculation: There are 24 x 40 = 960 hours in 40 days (and 40 nights). The height of Mount Everest (the highest mountain in the world) is 29,028 feet. In inches, this is 29,028 x 12 = 348,336 inches. Obviously the oceans would have to rise from sea level to this height. If we divide this by the number of hours, we get a rainfall of 348,336 /960 = 363 inches per hour, or 363 /60 = 6.0 inches per minute.