Mary earned scores of 88, 91, 75, and 72 on four science tests. Determine her score on the

fifth test if her average for the five tests was 81.

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Mary's score on the fifth test was 79.

Step-by-step explanation:

Mary's 1st score = 88 Mary's 2nd score = 91 Mary's 3rd score = 75 Mary's 4th score = 72 Mary's 5th score = x Mary's average score for the five tests = 81

Let's solve for x, this way:

Mary's average score for the five tests = (Mary's 1st score + Mary's 2nd score + Mary's 3rd score + Mary's 4th score + Mary's 5th score) / 5

Replacing with the values given:

81 = (88 + 91 + 75 + 72 + x) / 5

81 * 5 = 326 + x

405 = 326 + x

- x = 326 - 405

x = 79