A tin of oil was $\frac{4}{5}$ full. When 6 bottles of oil were taken out and four bottles of oil were poured into it, it was $\frac{3}{4}$ full. How many bottles of oil can the tin contain?
Answer
Answer (as printed):
Explanation
Suppose $x$ bottles can fill the tin completely. Then, $\frac{4}{5} x-\frac{3}{4} x=(6-4) \Leftrightarrow \frac{x}{20}=2 \Leftrightarrow x=40$. ∴ Required number of bottles $=40$.
Explanation as extracted from the printed page; notation may be imperfect.