SOLUTION: On his last three math tests, mark scored 85,95, and 80. What grade must he get on his next test to have an average of 90 for all four tests?

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Question 273290: On his last three math tests, mark scored 85,95, and 80. What grade must he get on his next test to have an average of 90 for all four tests?
Answer by JBarnum(2146) About Me  (Show Source):
You can put this solution on YOUR website!
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%2885%2B95%2B80%2Bx%29%2F4=90 add the numbers u can
%28260%2Bx%29%2F4=90 multiply by 4 to both sides of = sign
%28%28260%2Bx%29%2Fcross%284%29%29cross%284%29=90%284%29
260%2Bx=360 subtract 260
x=100
so the student has to get a highlight%28100%29 on the next test to get an average of 90