Question 150536
(3*72+x*100)/(x+3)=88
(216+100x)/(x+3)=88
216+100x=88(x+3)
216+100x=88x+264
100x-88x=264-216
12x=48
x=48/12
x=4 more tests with grades of 100 should do it.
Proof:
(216+4*100)/(4+3)=88
(216+400)/7=88
616/7=88
88=88