[amp_mcq option1=”220 minutes” option2=”180 minutes” option3=”145 minutes” option4=”160 minutes” correct=”option2″]
The correct answer is (b).
Let $x$ be the original time taken by the train. If the train increases its speed by 12.5%, then the new time taken is $\frac{112.5}{100}x = \frac{27}{20}x$. Since the new time is 20 minutes earlier, we have $\frac{27}{20}x = x – 20$. Solving for $x$, we get $x = \boxed{180}$ minutes.
Option (a) is incorrect because it is the time taken by the train if it does not increase its speed. Option (c) is incorrect because it is the time taken by the train if it increases its speed by 25%. Option (d) is incorrect because it is the time taken by the train if it increases its speed by 50%.