The cost of gas for a truck is $3.59. The gas tank holds 28.2 gallons when empty, but it is 1/5 full now. How much will it cost to fill the tank?
Answer: $80.99 (80.9904 rounded to cents)
The tank needs 22.56 gallons to become full (80% of 28.2, because 1/5 is 20%). Now multiply $3.59 times 22.56.
An alternate method would be to calculate the cost of a full tank, then subtract 20%. The full tank ($3.59 times 28.2) is $101.238; do not round in the middle of the task. 20% of $101.238 is $20.2476. Subtract $20.2476 from $101.238 and you get $80.9904.
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