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A student has earned scores of 87, 81, and 88 on the first 3 of 4 tests. If the student wants an average (arithmetic mean) of exactly 87, what score must she earn on the fourth test?

Answer 1

Hazel Anglin

She must earn a score of #82# on her fourth test.

To have an average of #87#, if we call the 4th test results #f# then #color(white)("XXX")(87+81+88+f)/4 =87#

#color(white)("XXX")256+f=87xx4=348#

#color(white)("XXX")f=82#

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Answer 2

Jace Anderson

To find the score needed on the fourth test:

Let x be the score on the fourth test.

The average of the four tests should be 87.

(87 + 81 + 88 + x) / 4 = 87

(87 + 81 + 88 + x) = 87 * 4

87 + 81 + 88 + x = 348

x = 348 - (87 + 81 + 88)

x = 348 - 256

x = 92

Therefore, the student must earn a score of 92 on the fourth test.

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Answer from HIX Tutor

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.