during the first 20 km of a 50 km bicycle race, Rosa's average speed was 30 km/h. What must her average speed be during the remainder of the race if she is to finish the race in less than 1.5 hr.

Answer 1

First let's find out how long the first twenty kilometers took: 20 km/30 km/hr=40 minutes.

Then we do 90 minutes(1.5 hours)-40 minutes=50 minutes(5/6 of an hour)

Let's find out what speed Rosa needs to ride at to go thirty kilometers in fifty remaining minutes: 30km divided by 5/6 = 36 km/hr