A family travels by car from their home to the beach. For the first 2 hours they drive at 60 mph. For the third hour, they drive at 70 mph. For the last 2 hours they drive at 55 mph.
a) (5 pts) How far do they travel in 5 hours?
b) (5 pts) If the family car averages 31.7 mpg, how many gallons of gas would be needed for the trip to the beach? Round to the nearest tenth of a gallon.
c) (5 pts) If the current price of gas is $3.72, how much will it cost for the family to drive from home to the beach?

If a trip is driven 2 hours at 60 mph, 1 hour at 70 mph, and 2 hours at 55 mph, you want to know the length of the trip. You also want to know the amount of gas used if mileage is 31.7 mpg, and the cost of gas for the trip at $3.72 per gallon.

Distance

The distance is the sum of products of time and speed:

(2 h)(60 mi/h) +(1 h)(70 mi/h) +(2 h)(55 mi/h)

= 120 mi + 70 mi +110 mi = 300 mi

The family traveled 300 miles from their home to the beach.

Gallons

The amount of gas required for the trip is the ratio of miles to miles per gallon:

(300 mi)/(31.7 mi/gal) ≈ 9.464 gal ≈ 9.5 gal

About 9.5 gallons of gas would be needed for the trip.

Cost

The cost of gas for the trip is the product of the number of gallons and the cost per gallon:

(9.464 gal)($3.72/gal) ≈ $35.21

It will cost the family about $35.21 to drive from home to the beach.

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Additional comment

Usually, we only round calculation results at the end. Here, we used the "exact" value of required gallons for figuring the gas cost. If we used the rounded value of 9.5 gallons, the cost would be calculated as $35.34.