x+y=45
x+z=35
y+z=40
There were 20 people who answered A correctly, 25 people who answered B and 15 people who answered C.
The total score is 20*20+25*40+ 15*40=2000.
Because three people answered three correctly, and 14 people answered two correctly, the total number of people x+y+z must be three right and two right, so x+y+z=60 people minus multiple calculations (three correctly counted twice and two correctly counted once).
Get 60-2*3- 14=40 people.
Average score =2000/40=50.
Oh, I haven't done the problem for a long time