A37-mm automatic gun fires at the rate of 120 rounds of ammunition per minute, but must cool for 2 minutes after 100 rounds are fired. how many seconds will elapse between the firing of the first and last round when 120 rounds of ammunition are fired as rapidly as possible?

The solution for this problem will be computed by:
The first 100 rounds takes: 100 / 120 * 60 = 50 seconds Then adding 2 minutes cooling time = 120 seconds Final 20 rounds = 20 / 120 * 60 = 10 seconds 
Adding them all together:50 + 120 + 10 = 180 seconds which is equal to 3 minutes.