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  1. Chapter 8 Class 7 Comparing Quantities
  2. Serial order wise
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Ex 8.3, 7 (i) Chalk contains calcium, carbon and oxygen in the ratio 10:3:12. Find the percentage of carbon in chalk. Calcium : Carbon : Oxygen = 10 : 3 : 12 Total parts = 10 + 3 + 12 = 25 Percentage of carbon = (๐‘ƒ๐‘Ž๐‘Ÿ๐‘ก๐‘  ๐‘œ๐‘“ ๐‘๐‘Ž๐‘Ÿ๐‘๐‘œ๐‘›)/(๐‘‡๐‘œ๐‘ก๐‘Ž๐‘™ ๐‘๐‘Ž๐‘Ÿ๐‘ก๐‘ ) ร— 100 = 3/25ร— 100% = 3 ร— 100/25 % = 3 ร— 4% = 12% Ex 8.3, 7 (ii) If in a stick of chalk, carbon is 3g, what is the weight of the chalk stick? Given, Weight of Carbon = 3g Now, We know that Carbon 12% of chalk Weight of Carbon = 12% ร— Weight of chalk 3 = 12% ร— Weight of chalk 3 = 12/100 ร— Weight of chalk 12/100 ร— Weight of chalk = 3 Weight of chalk = 3 ร— 100/12 Weight of chalk = 100/4 Weight of chalk = 25 So, Weight of chalk is 25 g Weight of chalk = 3 ร— 100/12 Weight of chalk = 100/4 Weight of chalk = 25 So, Weight of chalk is 25 g

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Davneet Singh
Davneet Singh is a graduate from Indian Institute of Technology, Kanpur. He has been teaching from the past 8 years. He provides courses for Maths and Science at Teachoo. You can check his NCERT Solutions from Class 6 to 12.