Halfway through a cross-country meet, a runner's speed is 4 m/s. In the

last stretch, she increases her speed to 7 m/s. What is her change in

speed?

The change in her speed is 7 m/s - 4 m/s = 3 m/s.

Step-by-step explanation:

Speed is defined as the rate of change of distance with time.

i) Let the total distance of the cross country be x meters.

ii) The change in her speed is 7 m/s - 4 m/s = 3 m/s.