How to solve inverse equation problems

Sometime in UGC NET paper 1 , you have to solve inverse equation problems . So, understand these type question and utilize your mathematical reasoning for solving question . I am here taking one example :-

First example

If 3 men or 4 women can reap a field in 43 days , how long will 7 men and 5 women take to reap it
a) 21.5 days , b) 12 days c) 15 days or d) 10.5 days

This is question of inverse equation because more no. of men and women will reap in less time .
So, understand its solution

suppose men = A

women = B

under the condition 1

3A = 4 B because 3men or 4 women can reap a field in 43 days .


so it means 4 B can reap in 43 days

now B or one women can reap in 43 X 4 = 172 days .

Second condition of question

If 7 A + 5 B becomes together how many day will happen ?

Replace the value of A = 4B/3 in place of A

7 x 4B/3 + 5 B = 14.3 B

If a women ( 1B ) can reap in 172 days

Now 14.3 women will fastly so 172 days will be divided by 14.3
answer = 172/14.3 =12.02

It means 7 men and 5 women can reap the field in 12 day so b) is correct answer .