Question:
An alloy contains 30% copper, 42% nickel and rest zinc. Find the mass of zinc in 1 kg of alloy.
Solution:
Percentage of copper $=30 \%$
Percentage of nickel $=42 \%$
Percentage of zinc $=\{100-(30+42)\} \%$
= 28%
$\therefore$ Mass of zinc in $1 \mathrm{~kg}$ of the alloy $=\left(\frac{28}{100} \times 1\right) \mathrm{kg}=0.28 \mathrm{~kg}=280 \mathrm{~g}$