Exercise 48 Page 503

Let's recall that the average speed can be expressed as the sum of speeds in each hour of the trip divided by the number of hours of the trip. Average speed=sum of speeds in each hour/number of hours We are given that Jarod's average driving speed for a 5-hour trip was 58 miles per hour. We also know that during the first 3 hours, he drove 50 miles, and we are asked to find his average speed, s, during the last 2 hours. We can substitute these values into our equation to find s.

Average speed=sum of speeds in each hour/number of hours

SubstituteValues

Substitute values

58=50+50+50+ s+ s/5

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Solve for s

AddTerms

Add terms

58=150+2s/5

MultEqn

LHS * 5=RHS* 5

290=150+2s

SubEqn

LHS-150=RHS-150

140=2s

DivEqn

.LHS /2.=.RHS /2.

70=s

RearrangeEqn

Rearrange equation

s=70

The average speed for the last 2 hours of Jarod's trip was 70 miles per hour. This corresponds with answer F.