physics
posted by moon .
A car accelerates at a constant rate from zero to 20.5 m/s in 10 seconds and then slows to 15.9 m/s in 5 seconds. What is its average acceleration to the nearest tenth of a m/s2 during the 15 seconds?

The average acceleration during a period of time is the starttofinish velocity change, divided by the length of time.
In this case, that would be
(15.9 m/s)/15 s = 1.06 m/s^2