Question 469906
Because of a poor grade on the fifth and final test, Chris's test grade fell from 90.5 to 84.0. what did Chris score on the fifth test. Assume all tests are equally important.
<pre>
Let the last (poor) grade be x.

It's the same as if Chris's grade on each of the first four tests were
exactly 90.5.  So let's work the problem as though Chris's 5 grades were 

90.5, 90.5, 90.5, 90.5, and x

{{{(matrix(4,1,

average,
on,
all,
tests)) = (matrix(7,1,

sum,
of,
all,
5,
tests,
over,
5)) }}}

{{{84.0=(90.5+90.5+90.5+90.5+x)/5}}} 

{{{84.0=(362+ x)/5}}}

Multiply both sides by 5

{{{420 = 362 + x}}}

{{{58 = x}}}

Chris's poor 5th grade = 58

Edwin</pre>