Question

1. Chalk contains calcium, carbon and oxygen in the ratio $10:3:12$. Find the percentage of carbon in chalk.
2. If in a stick of chalk, carbon is $3$ g, what is the weight of the chalk stick?

Answer 1

(i) Ratio of calcium, carbon, and oxygen = $10: 3: 12$
As $10 + 3 +12 = 25$,
Therefore, percentage of carbon = $\frac{3}{25}\times100=12\%$

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(ii) Let the weight of the stick be $x$ $g$.
$12 \%$ of $x$ = $3$

$\frac{12}{100}\times x=3$

$x= 3\times \frac{100}{12}=25\;g$