Question 1170496
rate * time = distance


72 kmph * 45/60 hours = 54 kilometers.
84 kmph * 20/60 hours = 56 kilometers.


total distance is 110 kilometers.
total time is (45 + 40) / 60 = 85 / 60  = 1.4166666667 hours.
average speed is 110 kilometers / 1.4166666667 = 77.64705882 kmph.


she left 20 minutes earlier and arrived 25 minutes later.
her time for the trip was (20 + 45 + 40 + 25) = 130 minutes / 60 = 2.166666667 hours.


her average speed was 110 / 2.166666667 = 50.76923077 kmph.


you could do this with fractions and should get the same answer.


doing it with fractions, you get:


72 kmph for 45/60 hours = a distance of 54 kilometers.
84 kmph for 40/60 hours = a distance of 56 kilometers.


total distance is 110 kilometers.
total time is 85/60 hours.


she started 20 minutes earlier and arrived
 25 minutes later.
it took her a total time of 85 + 45 = 130/60 hours.


her average speed was 110 / (130/60) = 110 * 60 / 130 = 6600/130 kmph.


6600/130 = 50.76923077 kmph.
it's the same answer done with fractions for the intermediate calculations.