Question

Abby scored 87, 86, 93, and 89 on her first four history quizzes. What score does Abby need to get on her fifth quiz to have an average of exactly 91 on her history quizzes.?
A.94 B.98 C.100 D.90
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Answer 1

Answer:

(C) 100

Step-by-step explanation:

The average of a data set is just all the numbers added up divided by the amount of numbers.

If we already have 4 pieces of data and we're looking for one more, we have 5 data pieces.

This means that the sum of all of the numbers in the data set will be $91\cdot5=455$ if the mean is 91.

We can find the missing value by adding up what we know and subtracting from 455.

$87+86+93+89=355\\\\455-355=100$

So Abby needs a 100% on her fifth history quiz to have an average of 91 on all her quizzes.

Hope this helped!