math
posted by felicia on .
Tim wants his mean (average) quiz score in history class to be 90. His first 3 quiz scores were 86, 92, and 94. What score should he make on the 4th quiz in order to have a mean (average) quiz score of exactly 90?
I really need the answer ! PLZ PLZ PLZ ! cant figure it outtt !!!! ___

Nvmd yo ! I got it !

x1 + x2 + x3 = 86 + 92 + 94 = 272
( x1 + x2 + x3 + x4 ) / 4 = 90
( 272 + x4 ) / 4 = 90 Multiply both sides by 4
272 + x4 = 90 * 4
272 + x4 = 360
x4 = 360  272 = 88 
Tim wants his mean (average) quiz score in history class to be 90. His first 3 quiz scores were 86, 92, and 94. What score should he make on the 4th quiz in order to have a mean (average) quiz score of exactly 90?