Evian's average no five tests were 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?

Answer 1

If the low score was x and the high score was y, then

x+4*93 = 5*90
4*87.75 + y = 5*90

x+y = 5*90-4*93 + 5*90-4*87.75 = 177

Answer 2

Evian's average mark for all 5 tests was 90%.
this was the sum of the 5 test scores divided by 5.
the total mark for all 5 tests was therefore 90 * 5 = 450%.
similarly the total mark for the 4 highest test scores was 4 * 93 = 372%
similarly, the total mark for the 4 lowest test scores was 4 * 87.75 = 351%
subtract the 4 lowest test scores from the total test score to get the highest test score.
subtract the 4 highest test scores from the total test score to get the lowest test score.
you get the highest test score = 450 - 351 = 99%
you get lowest test score = 450 - 372 = 78%
the total of the highest test score and the lowest test score is 177%.