Suppose it took you 30 minutes less to drive the 40 miles ba

Suppose it took you 30 minutes less to drive the 40 miles back home after dinner at your parents\' house than it did for you to arrive there in rush - hour traffic. You drove about 15 mph faster on the way home. How fast did you drive each way (see Example 19)?

Solution

Lets assume he drove x mph towrds his parents house

Return journey x+15 mph

distance = 40 miles each side

40/x - 40/(x+15) = 30/60

40[ 1/x - 1/(x+16)] = 1/2

[15/(x(x+16)] = 1/80

15*80 = x(1+16)

x^2 +16x - 1200 =0

solve for x: x = 27.55 mph ; x = -43.55

neglect -ve x

So, the speed towards = 27.55 mph

speed on retrun journey = 42.55 mph