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Donna has scored 80, 80, 90, 77, and 78 on her previous five tests. What score does she need on her next test so that her average (mean) is 81?

Sagot :

To determine what score Donna needs on her next test to achieve an average of 81, follow these steps:

1. Identify the scores from Donna's previous tests:
Donna's scores are: 80, 80, 90, 77, and 78.

2. Calculate the sum of her previous test scores:
Add up the scores:
[tex]\[ 80 + 80 + 90 + 77 + 78 = 405 \][/tex]
So, the sum of the previous scores is 405.

3. Determine the number of tests including the next test:
Donna has already taken 5 tests. The next test will be her 6th test.

4. Calculate the total score needed to achieve the desired average:
Donna wants an average of 81 over 6 tests. Multiply the desired average by the total number of tests:
[tex]\[ 81 \times 6 = 486 \][/tex]
So, to have an average of 81 across 6 tests, the total score should be 486.

5. Find the score Donna needs on her next test:
Subtract the sum of her previous test scores from the total score needed:
[tex]\[ 486 - 405 = 81 \][/tex]
Therefore, Donna needs to score 81 on her next test to achieve an average of 81.

So, Donna needs to score 81 on her next test to have an average of 81.