Question 1174361
average=total/n
70=total/6 or total=420
80=total/6 or total=480

want the total grades to be >=420 and <480
The four grades add to 304. Two grades must therefore add between 116 and 176, and since they are equal between 58 and 88
58<=grade<88. This is the answer,
Can check
58 is -24  (counts twice)
76 is +6
95 is +25
56 is -14
77 is +7
The difference is 0
-
for average  80
88 is +16 (counts twice)
76 -4
95 +15
56 -24
77 -3
The difference is 0