Question

If $a:b=2:3$ and $b:c=4:7$ then the reciprocal ratio of $a:c$ is ____

• A. $8:21$
• B. $21:8$
• C. $7:4$
• D. $3:2$

Answer 1

Answer: (B)

$21:8$

$a:b=2:3$ and $b:c=4:7$
$\therefore a:c=\frac{a}{b}\times \frac{b}{c}=\frac{2}{3}\times \frac{4}{7}$
$=\frac{8}{21}$
$\therefore a:c=8:21$
$\therefore$ The reciprocal ratio of $a:c$ is $21:8$.