A, B and C do math problems. It is known that A does 7 more questions than B, C does 2 more questions than A and 30 more questions than B. How many questions have they done?
Solution: Let's assume that B did X questions and deduce them from the meaning of the questions:
(x+7)×2=x+30，
2x+ 14=x+30，
x = 6；
Answer: 10+7= 17 (Road);
C: 17×2=34 (road);
All:10+17+34 = 61(road);
They did 6 1 math problems.