proportion

Question

Nuala drives to her grandma’s. She drives at 20 miles per hour . The journey takes 50 minutes. How long would the journey take if if Nuala drove at 40 miles per hour?

Answer 1

Rate times Time equals distance

 

The distances are equal, Therefor:

 

(20 m.p.h.) (50 min ) = (40 m.p.h.) ( x min.)

 

                       1000 = 40X

 

                           25 = X

 

25 minutes

 

If she drives twice as fast, the time for the trip is half as long.

Answer 2

One hour is 60 minutes, so if she drives 20 miles per 60 minutes, she drives X miles in 50 minutes:

20 / 60 = X / 50, X = (50 x 20) / 60 = 16.67 miles. If she drives 40 miles in 60 minutes, she drives 16.67 miles in Y minutes, so: 40 / 60 = 16.67 / Y, Y = (16.67 x 60) / 40 = 25 minutes. This makes sense, since by doubling the speed, the time travelled is cut in half.