Allison's car holds 15 gallons of gas. on a long trip, she fills the tank completely twice. the first time it costs $2.50 a gallon. if she spends a total of $76.50 on gas, how much did gas cost per gallon for the second tank?

First, find out how much she spent the first time. To find that, multiply 15 (Because you know she filled the tank completely) by 2.50 (the price of each gallon) to get 37.50. Subtract this from the total price of 30 gallons that have been bought.

76.50-37.50= 39

Now, divide 39 by 15 (because you know they bought 15 gallons of gas). Then you will get 2.60.

This means that her second time filling her tank, she bought gas for $2.60. You can check this by multiplying 2.60*15 which equals 39 and multiplying 2.50*15 which equals 37.50 and adding them to get 76.50. 

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