• question_answer 20) (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 3 g, what is the weight of the chalk stick?

(i) Total of parts = 10 + 3 + 12 = 25 Per cent of carbon in chalk $=\frac{3}{25}\times 100%=12%$ (ii) Let the weight of the chalk stick of chalk be P. Then, 12% of P = 3 $\frac{12}{100}\times P=3$ $P=\frac{3\times 100}{12}=25g$ $P=25g$ Hence, the weight of the chalk stick is 25 g.