Question 987727
<pre>
It's the same as if she had made exactly 85 on each of the first four tests.
Suppose she needs to make N on the 5th test to have an average of 88:

{{{(85+85+85+85+N)/5}}}{{{""=""}}}{{{88}}}

{{{(340+N)/5}}}{{{""=""}}}{{{88}}}

Multiply both sides by 5

{{{340+N}}}{{{""=""}}}{{{440}}}

{{{N}}}{{{""=""}}}{{{100}}}

She'll have to make a perfect score.

Edwin</pre>