Question 29941
Let "x" be the number of questions where he received 2 points.
Let "y" be the number of questions where he received -1 points.
Then x+y=50
The x answers will gain him 2x points  (2 pts. for each x answer)
The y answers will lose him -y points  (lose -1 for each y answer)
Then 2x-y=40
You now have two eqations  and two unknows:
Add the two equations to get:
3x=90
x=30 (number of questions where he received 2 points)
Substiute that value into the 1st (or the 2nd) equation and solve for "y":
30+y=50
y=20 (number of questions where he lost a point)
Cheers,
Stan H.