A candidate was asked to find $\frac{7}{8}$ of a positive number. He found $\frac{7}{18}$ of the same by mistake. If his answer was 770 less than the correct one, then the original given number was
(a)1260
(b)1548
(c)6160
(d)None of these
Answer
Answer (as printed): D
Explanation
Let the given number be $x$. Then, $\frac{7}{8} x-\frac{7}{18} x=770 \Leftrightarrow \frac{63 x-28 x}{72}=770 \Leftrightarrow \frac{35 x}{72}=770$ $$\Leftrightarrow x=\left(\frac{770 \times 72}{35}\right)=1584 .$$
Explanation as extracted from the printed page; notation may be imperfect.