if there are 40 question and each question carrying 5 marks and each wrong attempt can deduct 3 marks. if someone secured 70 marks then how many question he has attempted

Answer 1

Poorly worded question.
Are we to assume that some questions were skipped, and no reward or penalty for skipped questions?
I will assume that.

rights ---- x
wrongs --- y
skipped -- 40-x-y)

5x - 3y + 0(40-x-y) = 70
5x - 3y = 72
y = (5x-70)/3 , clearly 14 ≤ x ≤ 40 , x+y ≤ 40
values of x that yield whole number values for y are:
x .... y
14 0
17 5
20 10
23 15
26 20 ----> not possible notice 26+20 > 40

possible number of questions attempted:
14 , 22, 36, or 38

checking one of them:
20, 10
number correct: 20
number wrong : 10
number attempted: 36
marks obtained = 20(5) - 6(10) = 70