In a school exam, 70% of the students passed in Mathematics, 75% passed in English, and 10% failed in both subjects. If 990 students passed in both subjects, how many students took the exam?

Explanation

1. 01

   Failed in Mathematics = 30%; failed in English = 25%; failed in both = 10%.

2. 02

   Failed in at least one subject = $30\% + 25\% - 10\% = 45\%$.

3. 03

   Passed in both = $100\% - 45\% = 55\%$.

4. 04

   55% of total = 990, so total = $\frac{990}{55} \times 100 = 1{,}800$.