$(i)$. 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?

AcademicMathematicsNCERTClass 7


$(i)$. Given ratio$=10:3:12$

Total part$=10+3+12=25$

Part of Carbon$=\frac{3}{25}$

Percentage of Carbon part in chalk$=\frac{3}{25}\times100=12$ % 

$(ii)$. Quantity of Carbon in chalk stick$=3\ g$

Let the weight of chalk be $x\ g$.

Then, $12$ % of $x=3$

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

$\Rightarrow x=\frac{3\times100}{12}=25\ g$

Hence the weight of the chalk stick is $25\ g$.
Updated on 10-Oct-2022 13:35:12