Question

A student has gotten the following grades on his tests. What is the minimum gradehe must get on the last test in order to have an average of 84?89, 92, 71, 78

Answer 1

The average may be obtained by adding all the given values divided by the number of values. Since 4 of the 5 values are given and the given average is 84, we may substitute the given values in the following formula.

$\overline{x}=\frac{x_1+x_2+x_3+x_4+x_5}{5}$

Thus, we will obtain the following.

$84=\frac{89+92+71+78+x_5}{5}$

To solve for the missing value, find the sum of the four addends.

$84=\frac{330+x_5}{5}$

Multiply both sides of the equation by 5.

$420=330+x_5$

And subtract both sides of the equation by 330.

$\begin{gathered} 420-330=x_5 \\ 90=x_5 \end{gathered}$

Thus, the last score should be 90.