Question 835403
First find the grade on the test that will produce an average
grade of 75.
Set x = the grade on the 5th test.

{{{(64 + 86 + 71 + 90 + x)/5=75}}}
{{{(311 + x)/5=75}}}
multiply each side by 5
{{{311 + x=75*5}}}
{{{311 + x=375}}}
add -311 to each side
{{{x=375-311}}}
{{{x=64}}}
So a grade of 64 produces an average of 75
and a grade of 64 or above will produce
an average greater than or equal to 75