Question

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

Answer 1

i) Chalk contains calcium, carbon and oxygen in the ratio of

$10:3:12$

$\therefore$ Let $x$ be common ratio.

Calcium $=10x$

Carbon $=3x$

oxygen $=12x$

$\therefore \%$ of carbon $=\frac{3x}{10x+3x+12x}\times 100$

$=\frac{3x}{25x}\times 100$

$\therefore \%$ of carbon $=12\%$

ii) Now, weight ofcarbon is $3g$
Let total mass of chalk is $x$ gram
$\Rightarrow 12\%$ of $x=3$
$\Rightarrow \frac{12}{100}\times x=3$
$\therefore x=\frac{300}{12}=25$
$\therefore$ weight is $25$ grams