Mr. Smith traveled to a city 300 miles from his home to attend a meeting. Due to car trouble, his average speed returning was 6 mph less than his speed going. If the total time for the round trip was 9 hours, at what rate of speed did he travel to the city

The speed at which he traveled to the city is 69.8 mph

Step-by-step explanation:

Let x represent the speed at which he traveled to the city.

Mr. Smith traveled to a city 300 miles from his home to attend a meeting.

Time = distance/speed

Time taken to travel to the city is

300/x

Due to car trouble, his average speed on returning was 6 mph less than his speed going. This means that the speed at which he returned is (x - 6) mph. Time taken to return from the city is

300/(x - 6)

If the total time for the round trip was 9 hours, it means that

300/x + 300/(x - 6) = 9

Cross multiplying by x(x - 6), it becomes

300(x - 6) + 300x = 9x(x - 6)

300x - 1800 + 300x = 9x² - 54x

9x² - 54x - 300x - 300x - 1800 = 0

9x² - 654x -1800 = 0

Applying the general quadratic equation,

x = [- b ± √(b² - 4ac)]/2a

From the equation given,

a = 9

b = - 654

c = 1800

Therefore,

x = [- - 654 ± √(- 654² - 4 × 9 × 1800)]/2 × 9

x = [654 ± √(427716 - 64800)]/18

x = [654 ± √362916.4]/18

x = (654 + 602.4)/2 or x = (654 - 602.4)/18

x = 1256.4/18 or x = 51.6/18

x = 69.8mph or x = 2.9 mph

The speed at which he traveled to the city is 69.8 mph

By checking,

Time spent travelling to the city = 300/69.8 = 4.3 hours

Time spent returning =

300/(69.8 - 6) = 4.7 hours

4.3 + 4.7 = 9 hours