How do you find the score for this problem?

Question

Monica had a mean score of 77 after 3 tests. What score does she need on the fourth test to raise her score to 80? Show work

Answer 1

Mean is( x1+x2+x3) /3=77

total x1+x2+x3= 77*3 =231

New mean = (x1+x2+x3+x4)/4=80

Since we know the sum of the x1+x2+x3 we can replace (231+x4)/4=80

231+x4= 80*4

231+x4=320

x4=320-231=89 so new score is 89.

Hope this helps...