To find out what Jacob needs to score on his fifth test to achieve a mean of 80, we can start by calculating the total score he needs after five tests.
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Calculate the total score needed for a mean of 80: \[ \text{Total score needed} = \text{Mean} \times \text{Number of tests} = 80 \times 5 = 400 \]
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Calculate Jacob's current total score after four tests: Given that his mean score after four tests is 78: \[ \text{Current total score} = \text{Mean} \times \text{Number of tests} = 78 \times 4 = 312 \]
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Find out what he needs on the fifth test: We can determine the score needed on the fifth test by subtracting his current total score from the total score needed: \[ \text{Score needed on fifth test} = \text{Total score needed} - \text{Current total score} = 400 - 312 = 88 \]
So, Jacob needs to score 88 on his fifth test to achieve an average of 80.