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AlgebraEasyFuel remaining from a two-variable equation

Algebra practice question

The fuel f, in litres, left in a car's tank after it has driven d kilometres is given by f = 40 − 0.1d. How many litres are left after 100 kilometres?

Answer: 30

f = 40 − 0.1(100) = 40 − 10 = 30.

Common wrong answers

If you answered 10
10 is the fuel used, not the fuel left.
If you answered 50
50 adds instead of subtracting.
If you answered 39.9
39.9 subtracts 0.1 once instead of 0.1 × 100.

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