One junior student is asked to divide half a number by 6 and the other half by 4 and then add the quantities. Instead of doing so, the student divides the given number by 5. If the answer is 4 short of the correct answer, then the number is
(a)320
(b)360
(c)400
(d)480
Answer
Answer (as printed): D
Explanation
Let the number be $2 x$. Then, $\left(\frac{x}{6}+\frac{x}{4}\right)-\frac{2 x}{5}=4 \Leftrightarrow \frac{10 x+15 x-24 x}{60}=4 \Leftrightarrow x=240$. Hence, required number $=2 x=480$.
Explanation as extracted from the printed page; notation may be imperfect.