Question

Find the sum:
$\frac{3}{28}+\frac{1}{21}$

• A. $\frac{17}{84}$
• B. $\frac{13}{84}$
• C. $\frac{11}{84}$
• D. $\frac{15}{84}$

Answer 1

The correct option is B

$\frac{13}{84}$

To find the value of $\frac{3}{28}+\frac{1}{21}$, first we have to find the LCM of 28 and 21.
$\begin{array}{cc}2& 28,21\\ 2& 14,21\\ 3& 7,21\\ 7& 7,7\\ & 1,1\end{array}$
LCM of 28 and 21 $=2\times 2\times 3\times 7=84$

$\frac{3}{28}+\frac{1}{21}$ $=\frac{3\times 3}{28\times 3}+\frac{1\times 4}{21\times 4}=\frac{9+4}{84}=\frac{13}{84}$