Question 273290
finding the average is where you add all the numbers up and divide by the number of numbers u have. so for this problem he will have 4 grades that will make him an average of 90.
so{{{(85+95+80+x)/4=90}}} add the numbers u can
{{{(260+x)/4=90}}} multiply by 4 to both sides of = sign
{{{((260+x)/cross(4))cross(4)=90(4)}}}
{{{260+x=360}}} subtract 260
{{{x=100}}}
so the student has to get a {{{highlight(100)}}} on the next test to get an average of {{{90}}}