Hello, while you are running heart beating 2400 times in 20 minutes, so we can say that is equal to:
2400 times / 20 minutes * 1 min / 60 seconds, thus,
(2400 times * 1 min) / (20 min * 60 seconds)
2400 times / 1200 seconds = 2 times / second, the heart beats 2 times per second when you are running. For the case when we are resting, then:
17 times / 15 seconds --> 17/15 aprox. 1.1333... , so the heart beats 1.13 times aprox. when we are resting.
Thus, (rate of beating running) - (rate of beating resting) = 2 - 1.13 = 0.87
So, we can say that the heart beats 0.83 times more (aprox.) when we are running than when we are resting. I hope I help you. Sorry for my English.