# Key made scores of 81, 76, 82 on three quizes. what is the least she can make on the fourth quiz to have an average of at least 80? 75 78 81 85 90

2
by iamaqt13

2014-12-31T20:43:35+08:00
She needs a score of 81 on the fourth quiz to have an average of 80.
2014-12-31T21:04:22+08:00

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To answer this question, we need to use the linear equation:

We all know that to get the average using the mean, we add all the terms and then, divide it by the number of terms.

Okay, let x be the least score she can make in the 4th quiz:

The symbol " " means at least and  means at most.

It becomes:

We multiply 4 to both sides to cancel the denominator

80 x 4 =320

So, it is:
239 + x  320

We subtract 239 to both sides so that only thing that will be left in "239 + x" is only "x."
239 + x -  239  320 - 239
x  81

Therefore, the least score she can make on the 4th quiz is 81.