Question

Joey wants to get a 90 test average in Science. He has already had two tests and he earned
a 91 and 85 on those tests. Write and solve an equation to find out what Joey needs to get on
the third test in order to have a 90 test average in Science.

Answer 1

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Answer 2

Answer:

Joey must get a score of 94 to have a average test score of 90.

Step-by-step explanation:

Joey wants a average score of 90.

He already scored 91 and 85 on the previous two tests, and wants to know the score to get a 90 as an average.

Set the equation:

Average = (score of known tests + x)/(amount of tests in all).

Note that: x = score of the next test.

First, Plug in the corresponding numbers to the corresponding terms/variables:

90 = (91 + 85 + x)/(3)

Simplify. Isolate the variable, x. Note the equal sign, what you do to one side, you do to the other. Do the opposite of PEMDAS.

First, multiply 3 to both sides:

90(3) = (91 + 85 + x)/(3) * 3

270 = 91 + 85 + x

Isolate the variable x. Combine like terms:

270 = (91 + 85) + x

270 = 176 + x

Subtract 176 from both sides:

270 (-176) = 176 (-176) + x

x = 270 - 176

x = 94

Joey must get a score of 94 to have a average test score of 90.

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