ABC26GN1674 · Problems on Numbers

Subject: General Aptitude · Chapter: Problems on Numbers · Exam: · Marks: · Difficulty:

A positive number when decreased by 4 is equal to 21 times the reciprocal of the number. The number is

(a)3

(b)5

(c)7

(d)9

Answer

Answer (as printed): C

Explanation

Let the number be $x$. Then, $x-4=\frac{21}{x} \Leftrightarrow x^{2}-4 x-21=0$ $$\Leftrightarrow(x-7)(x+3)=0 \Leftrightarrow x=7 \text {. }$$

Explanation as extracted from the printed page; notation may be imperfect.