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Erin has written three tests for her math class. She calculates the average of hermarks on the first two tests. This average is then averaged with her third testmark to get 80%. She then calculates the average of her marks on the last twotests. This average is then averaged with her first test mark to get 83.5%.Finally, she calculates the average of her marks on the first and third tests. Thisaverage is then averaged with her second test mark to get 84.5%.Her fourth test is coming up and after writing this test she wants her overallaverage for the four tests to be exactly 86%. If all four tests are out of 100 marks,what mark does Erin need to get on her fourth test in order for her overallaverage to be exactly 86%?

Respuesta :

fichoh

To obtain an overall average of 86%, a score of 96 is required on her 4th test.

Let the required score on her fourth test = t

The required average = 86%

Initial scores : 80% + 83.5% + 84.5%

Average = ΣX/ (fx)

fx = total score obtainable = 4 × 100 = 400

ΣX = sum of scores

Average = 86%

0.86 = ((80 + 83.5 + 84.5 + t) / 400)

86 = (248 + t) / 400

400 × 0.86 = 248 + t

344 = 248 + t

344 - 248 = t

96 = t

In other to obtain an overall average of 86%, she has to score 96 in her 4th test.

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