Circular gears P and Q start rotating at the same time at constant speeds.

Circular gears P and Q start rotating at the same time at constant speeds. Gear P makes 10 revolutions per minute and Gear Q makes 40 revolutions per minute. How many seconds after the gears start rotating will gear Q have made exactly 10 more revolutions than gear P?

Quiz

Answer/Solution

20

Steps/Work

Gear Q makes 30 more revolutions each 60 seconds.
The time to make 10 = 30/3 more revolutions is 60/3 = 20 seconds.
The answer is D.