How much would I spend in a week if I average 25 km/day, get a mileage of 30 miles per US gallon, and petrol costs €1.26/L with a conversion rate of €1= $1.26?

1 Answer
Ernest Z.
Jun 21, 2014

You would spend $95.10.

You use a series of conversion factors.

There are many conversions, so let's break it into parts.

Calculate the gallons used

1 week × #(7"days")/(1"week") × (125"km")/(1"day") × (1"mi")/(1.60934"km") × (1"gal")/(30.0"mi")# =

18.123 gal (three significant figures plus two guard digits)

Calculate the cost

18.123 gal × #(3.78541"L")/(1"gal") × (€ 1.10)/(1"L") × ($ 1.26)/(€ 1)# = $95.10

The answer has only three significant figures, so it is precise only to the nearest
10 ¢.

Notice how the conversion factors are set up so they cancel to give the desired units at the end.

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