If 21a7 is divisible by 9, then which digit can replace the letter a in the 4-digit [3M] number 21a7?

The circumference of a redwood tree trunk is 20π ft, and it is 100 ft tall. what is the approximate volume of the redwood tree trunk? 1,000π ft3 10,000π ft3 4,000π ft3 40,000π ft3

What is the result of adding the system of equations? 2x+y=4 3x-y=6

A50% increase followed by 33 1/2% decrease