Subject: General Aptitude · Chapter: Ratio and Proportion · Exam: · Marks: · Difficulty:
The ratio between the third proportional of 12 and 30 and mean proportional of 9 and 25 is
(a)2 : 1
(b)5 : 1
(c)7 : 15
(d)9 : 14
Answer
Answer (as printed): B
Explanation
Let the third proportional to 12 and 30 be $x$. Then, $12: 30:: 30: x \quad \Leftrightarrow \quad 12 x=30 \times 30$ $$\Leftrightarrow \quad x=\frac{(30 \times 30)}{12}=75 .$$ ∴ Third proportional to 12 and $30=75$. Mean proportional between 9 and $25=\sqrt{9 \times 25}=15$. $$\text { ∴ } \text { Required ratio }=75: 15=5: 1 .$$
Explanation as extracted from the printed page; notation may be imperfect.