A student has an average of 78 on seven chapter tests. If the student's scores on six of the tests are 76, 74, 76, 80, 83, and 91, what was the score on the remaining test? 80 66 78 79

The score is 66

Step-by-step explanation:

Say the unknown score is x

Average = Total score/no of occurrence

78 = (x + 76 + 74 + 76 + 80 + 83 + 91) / 7

78 * 7 = x + 76 + 74 + 76 + 80 + 83 + 91

546 = x + 480

546 - 480 = x

66 = x

∴ x = 66