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Answer :

Given:

Average of test is 85.2

First four test grade is : 81, 87, 79, 93

let fifth test grade is "x"

so average is:

[tex]A\mathrm{}V\mathrm{}=\frac{x_1+x_2+x_3+x_4+x_5}{5}[/tex][tex]\begin{gathered} 85.2=\frac{81+87+79+93+x}{5} \\ 5\times85.2=81+87+79+93+x \\ 426=340+x \\ x=426-340 \\ x=86 \end{gathered}[/tex]

So the fifth test grades is 86.

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