Keiko has scored 86, 91, 86, 61, and 87 on her previous five tests. what score does she need on her next test so that her average (mean) is 84?

X= grade on next test

Add up all scores, divide by 6 and this equals the average of 84

(86 + 91 + 86 + 61 + 87 + x)/6= 84
add in parentheses

(411 + x)/6= 84
multiply both sides by 6

411 + x= 504
subtract 411 from both sides

x= 93

ANSWER: 93 is needed on the next test to have an average of 84

Hope this helps! :)