the average can be calculated by adding the scores together and then dividing by the number of scores.
we can set up an equation:
let x = test score needed on next test
(72+72+80+x)/4 = 71
multiply both sides by 4
72+72+80+x = 284
add like terms
224+x=284
subtract 224 from both sides
x=60
she will need a 60 for her average to be 71
