Subject: General Aptitude · Chapter: Ratio and Proportion · Exam: · Marks: · Difficulty:
$S$ varies directly as $R$ and $T$ varies inversely as $R$. At some particular time, $R=20, S=40$ and $T=10$. If $S$ is changed to 20, then the value of $T$ would be equal to
(a)10
(b)20
(c)40
(d)80
Answer
Answer (as printed): B
Explanation
$S \propto R$ and $T \propto \frac{1}{R} \Rightarrow S = kR$ and $T = \frac{m}{R}$ for some constants $k$ and $m$. When $R = 20, S = 40$ and $T = 10$: $S = kR \Rightarrow 40 = 20k \Rightarrow k = 2$. And $T = \frac{m}{R} \Rightarrow 10 = \frac{m}{20} \Rightarrow m = 10 \times 20 = 200$. When $S = 20$, $20 = 2R \Rightarrow R = 10$. And $T = \frac{200}{R} = \frac{200}{10} = 20$.
Explanation as extracted from the printed page; notation may be imperfect.