If $20 \%$ of $A=B$ and $40 \%$ of $B=C$, then $60 \%$ of ( $A+B$ ) is
(a)30\% of C
(b)60\% of $C$
(c)75\% of C
(d)None of these
Answer
Answer (as printed): D
Explanation
$\frac{20}{100} A=B$ and $\frac{40}{100} B=C \Rightarrow \frac{1}{5} A=B$ and $\frac{2}{5} B=C$ $$\Rightarrow A=5 B \text { and } B=\frac{5}{2} C \Rightarrow A=\frac{25}{2} C \text { and } B=\frac{5}{2} C \text {. }$$ $\therefore 60 \%$ of $(A+B)=\frac{60}{100}\left(\frac{25}{2} C+\frac{5}{2} C\right)$ $$=\frac{60 \times 15}{100} C=\frac{900}{100} C=900 \% \text { of } C .$$
Explanation as extracted from the printed page; notation may be imperfect.