Question

A motorist makes a trip of 180 miles . For the first 90 miles she drives at a constant speed of 30 mph at what constant speed must she drive the remaining distance if her average speed for the total trip is to be 40 mph

Answer 1

Remaining Distance = 180miles-90miles= 90miles
Time taken for first part of her journey= 90miles / 30miles/h= 3hours
To have average speed of 40mph,
Let the time taken for second part be xh
180 / 3h+xh =40
3+x= 4.5h
x =1.5h
Constant speed she must drive = 90miles / 1.5h = 60mph