Mr. Jackson traveled to a city 170 miles from his home to attend a meeting. Due to car trouble, his average speed returning was 8mph less than his speed going. If the total time for the round trip was 7 hours, at what rate of speed did he travel to the city? (Round your answer to the nearest tenth.)

the average speed at which he traveled to the city is 52.9 mph

Step-by-step explanation:

Let x represent the average speed at which he traveled to the city. Due to car trouble, his average speed returning was 8mph less than his speed going. It means that the speed at which he returned is (x - 8) mph.

Time = distance/speed

Assuming the distance travelled to and from the city is the same(170 miles), then

Time spent in travelling to the city is

170/x

Time spent in travelling back from the city is

170/(x - 8)

If the total time for the round trip was 7 hours, it means that

170/x + 170/(x - 8) = 7

Multiplying both sides of the equation by x(x - 8), it becomes

170(x - 8) + 170x = 7x(x - 8)

170x - 1360 + 170x = 7x² - 56x

7x² - 56x - 170x - 170x + 1360 = 0

7x² - 396x + 1360 = 0

Applying the general formula for solving quadratic equations which is expressed as

x = [- b ± √(b² - 4ac)]/2a

From the equation given,

a = 7

b = - 396

c = 1360

Therefore,

x = [- - 396 ± √(- 396² - 4 × 7 × 1360)]/2 × 7

x = [396 ± √(156816 - 38080)]/14

x = [396 ± √118736]/14

x = (396 + 344.58)/14 or x = (396 - 344.58)/14

x = 52.9 or 3.7

Checking both values of x,

For x = 52.9

170/52.9 + 170/(52.9 - 8) = 7

= 3.2 + 3.8 = 7

Therefore, x = 52.9 mph

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