Maria has taken four chemistry tests and have an average (arithmetic mean) score of 80. IF the scores a 90 on her fifth chemistry test, what is her average for these five tests?

Options

A. 80
B. 81
C. 82
D. 84

Answer

To find Maria's average score after taking five chemistry tests, we can follow these steps:

### Step 1: Calculate the total score for the first four tests.
Given that the average score for the first four tests is 80, we can calculate the total score for these tests using the formula for average:

\[ \text{Average} = \frac{\text{Total Score}}{\text{Number of Tests}} \]

Let \( S \) be the total score for the first four tests. Then we have:

\[ 80 = \frac{S}{4} \]

Multiplying both sides by 4 gives:

\[ S = 80 \times 4 = 320 \]

### Step 2: Add the score of the fifth test.
Maria scores 90 on her fifth test. We add this score to the total score from the first four tests:

\[ \text{Total Score for 5 tests} = S + 90 = 320 + 90 = 410 \]

### Step 3: Calculate the new average for the five tests.
Now we can find the new average score for all five tests:

\[ \text{New Average} = \frac{\text{Total Score for 5 tests}}{\text{Number of Tests}} \]

Substituting the values we found:

\[ \text{New Average} = \frac{410}{5} \]

Calculating this gives:

\[ \text{New Average} = 82 \]

### Conclusion:
Maria's average score for the five tests is **82**.

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