(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) Given ratio = 10 : 3 : 12
Total part = 10 + 3 + 12 = 25
Part of Carbon = 3/25
Percentage of Carbon part in chalk = 3/25×100 = 12%

(ii) Quantity of Carbon in chalk stick = 3 g
Let the weight of chalk be x g.
Then, 12% of x = 3
⇒ 12/100 X x=3
⇒ x = 3×100/12 = 25 g
Hence, the weight of chalk stick is 25 g.

lass 7 Maths Chapter 8 Exercise 8.3

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