Evian's average on five tests was 90%. The average of the four highest test scores was 93%, and the average of the four lowest test scores was 87.75%. What was the sum of the lowest mark and the highest mark?
(h + s + l )/5 = 90 or h+s+l = 450 where h = hi score s = 3 middle scores l = low score
(h +s)/4 = 93 or h+s = 372 or h= 372-s
(l+s)/4 =87.75 or l+s = 351 or l = 351-s
Take the last 2 red equations and sustitute into the first red equation:
372-s + s + 351-s = 450
Now (l +s)/4 = 87.75 so l = 78
and (h+s)/4 = 93 so h = 99 h+l = 177