When a particular number is subtracted from each of 7, 9, 11 and 15, the resulting numbers are in proportion… · ABC26GN3119
Subject: General Aptitude · Chapter: Ratio and Proportion · Exam: C.P.O. 2007
When a particular number is subtracted from each of 7, 9, 11 and 15, the resulting numbers are in proportion. The number to be subtracted is
(a)1
(b)2
(c)3
(d)5
Answer
Answer (as printed): C
Explanation
Let the required number be $x$. Then, $\frac{7-x}{9-x}=\frac{11-x}{15-x} \Rightarrow(7-x)(15-x)=(11-x)(9-x)$ $$\Rightarrow 105-22 x+x^{2}=99-20 x+x^{2} \Rightarrow 2 x=6 \Rightarrow x=3 .$$
Explanation as extracted from the printed page; notation may be imperfect.