Jon decides to take up baseball. He can throw a fastball at 80 miles per hour.  He goes through intense training 4 times for 4 weeks each time and at the end of the last one he can throw a ball 20% faster. How much speed (in mph) did he gain per week, assuming he gained an equal amount of speed (in mph) each week?
Let's think step by step below.
1
He threw the ball 80 *.

2 = 16 mph faster.

He was training for 4 * 4 = 16 weeks.

So he gained 16 / 16 = 1 mph per week.

.

Therefore, the answer is 1