A stationary engine has enough fuel to run 12 hours when its tank is $\frac{4}{5}$ full. How long will it run when the tank is $\frac{1}{3}$ full?
(a)Less than 2 hours
(b)2 hours
(c)3 hours
(d)4 hours
(e)5 hours
Answer
Answer (as printed): E
Explanation
Clearly, more fuel, the longer will the engine run. $$\therefore \quad \frac{4}{5}: \frac{1}{3}:: 12: x \text { or } \frac{4}{5} x=\frac{1}{3} \times 12=4 \text { or } x=4 \times \frac{5}{4}=5 .$$
Explanation as extracted from the printed page; notation may be imperfect.