Answer:
Her average speed is 45 mph
Step-by-step explanation:
Let the average speed be x mph
Time taken complete the journey = distance/ average speed
Time = 300/x
Now , at 9 mph less, she could have only traveled 240 miles in same time
At 9 mph less, the average speed is x-9
so the time would be 240/x-9
since the time is same as before;
300/x = 240/x-9
Divide both sides by 60
5/x = 4/x-9
Cross multiply
5(x-9) = 4(x)
5x - 45 = 4x
5x -4x = 45
x = 45 mph
