math
posted by Tricia on .
A student has a mean score of 88 on five tests taken. What score must she obtain on her next test to have a mean (average) score of 80 on all six tests?

Mean score of tests :
( x1 + x2 + x3 + x4 + x5 ) / 5 = 88 Multiply both sides by 5
x1 + x2 + x3 + x4 + x5 = 88 * 5
x1 + x2 + x3 + x4 + x5 = 440
Mean score of six tests :
( x1 + x2 + x3 + 4 + x5 + x6 ) / 6 = 80
[ ( x1 + x2 + x3 + 4 + x5 ) + x6 ] / 6 = 80
( 440 + x6 ) / 6 = 80 Multiply both sides by 6
440 + x6 = 80 * 6
440 + x6 =480
x6 = 480  440
x6 = 60 
( x1 + x2 + x3 + x4 + x5 + x6 ) / 6 = 80

x6 = 480  440
x6 = 40