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?

Solution

## a) Chalk contains calcium, carbon and oxygen $$10 : 3 : 12$$$$\therefore$$ Let $$x$$ be common ratio .Calcium $$= 10x$$Carbon $$= 3x$$oxygen $$=12x$$$$\therefore \%$$ of carbon $$=\dfrac{3x}{10x+ 3x+12x} \times 100$$$$=\dfrac{3x}{25x} \times 100$$$$\therefore \%$$ of carbon $$= 12\%$$b) Now, carbon is $$3g$$$$\therefore$$ Let total mass is $$x$$ gram $$\therefore 12\%$$ of $$x= 3$$$$\therefore \dfrac{12}{100} \times x =3$$ $$\therefore x =\dfrac{300}{12} =259$$$$\therefore$$ wight is $$25$$ grams Mathematics

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