Question

12 : 21 and 72 :126 are in proportion. Which of the following is correct?

• A. $72\times 126=21\times 12$
• B. $12\times 126=21\times 72$
• C. $12\times 72=21\times 126$
• D. None of these

Answer 1

The correct option is B

$12\times 126=21\times 72$

If a:b and c:d are in proportion then
$\frac{a}{b}=\frac{c}{d}$
On cross multiplication,
$ad=bc$.
Similarly if 12 :21 and 72 :126 are in proportion then
$12\times 126=21\times 72$