Question

A man spends 10% of his income on rent and 55% of household expenses and finds that he has $700 left. How much does he earn per month?

Answer 1

The man has spent 10% + 55% = 65% of his income.
That means he has 35% of his income left over.

The question is REALLY asking "$700 is 35% of what number?"

So it's basically asking you to solve 0.35x = 700