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# (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:**

According to the question,

The ratio of calcium, carbon and oxygen is 10:3:12.

Parts of carbon = 3

Sum of all parts = 10 + 3 + 12 = 25

Percentage of carbon = (Parts of carbon / Sum of all parts) × 100

= 3 / 25 × 100

= 12%

(ii) Carbon in the stick of chalk = 3 g,

Also, we know that carbon percentage in the chalk is 12%.

This means 12% of carbon = 3 g

Let the total weight of the chalk be Q

Hence, 12/100 × Q = 3

Total weight (Q) = 3 × 100/12 = 25 g

**☛ Check: **NCERT Solutions for Class 7 Maths Chapter 8

**Video Solution:**

## (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?

Class 7 Maths NCERT Solutions Chapter 8 Exercise 8.3 Question 7

**Summary:**

(i) Chalk contains calcium, carbon and oxygen in the ratio 10:3:12. Percentage of carbon in chalk is 12% (ii) If in a stick of chalk, carbon is 3g, the weight of the chalk stick is 25 g.

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