# Math Help - Finite Math

1. ## Finite Math

A student has an average of 92 after 3 tests. He scores 77 on the 4th test.

What score would he need to make on the 5th test to have an average of

90? Please show the formula used to get to the final answer. THANKS!!!!

2. Originally Posted by Susan Campbell
A student has an average of 92 after 3 tests. He scores 77 on the 4th test.

What score would he need to make on the 5th test to have an average of

90? Please show the formula used to get to the final answer. THANKS!!!!
You don't want a formula you need to be shown how to approach problems so that you can tackle ones that you have never seen before.

If the mean after the 5-th test is $90$ then:

$\frac{s_1+s_2+s_3+s_4+s_5}{5}=90$

where $s_i$ is the score on the $i$-th test.

You are told that $s_4=77$, you are also told that the mean of the first three tests is $92$, so:

$\frac{s_1+s_2+s_3}{3}=92$

So:

${s_1+s_2+s_3}=92\times 3=276$

Combining these we have:

$\frac{s_1+s_2+s_3+s_4+s_5}{5}=\frac{(s_1+s_2+s_3)+ s_4+s_5}{5}=\frac{276+77+s_5}{5}=90$

From which you can find the required $s_5$.

RonL