S.chand publication New Learning Composite mathematics solution of class 7 Chapter 8 Percentage and Its Applications Exercise 8E

Exercise 8E

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Q1 | Ex-8E |Class 7 |S.Chand | New Learning Composite maths |Percentage and Its Applications |Ch-7 |myhelper

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Question 1

Ravi’s class has 18 boys and 12 girls. What is its percentage composition?

Sol :
∴Percentage of boys$=\frac{18}{30}\times 100$=60%

∴Percentage of girls$=\frac{12}{30}\times 100$=40%

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Q2 | Ex-8E |Class 7 |S.Chand | New Learning Composite maths |Percentage and Its Applications |Ch-7 |myhelper

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Question 2

Chalk contains 10% calcium, 3% carbon and 12% oxygen. Find the amount of carbon and calcium (in grams) in 2 and $\frac{1}{2}$ kg of chalk.

Sol :

Amount of carbon$=\left(2\frac{1}{2}\times \frac{3}{100}\right)$ kg

$=\frac{6}{2}\times \frac{3}{100}=\frac{3}{40}$

∴Amount of calcium$=\left(2\frac{1}{2}\times \frac{10}{100}\right)$ kg

$=\left(\frac{5}{2} \times \frac{18}{100}\right)=\frac{1}{4}$

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Q3 | Ex-8E |Class 7 |S.Chand | New Learning Composite maths |Percentage and Its Applications |Ch-7 |myhelper

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Question 3

An alloy contains 4% tin, 1% zinc and the remaining copper.

(a) What is the percentage composition of the alloy?

Sol :

Percentage of tin=4%

Percentage of zinc=1%

Percentage of copper=(100-5)=95%

(b) Find the mass (in kg) of each metal in 5 tonnes of the alloy.

Sol :

5 tonnes=5000 kg

Mass of tin $=\left(5000 \times \frac{4}{100}\right)$=200 kg

Mass of zinc $=\left(5000 \times \frac{1}{100}\right)$=50 kg

Mass of copper $=\left(5000 \times \frac{95}{100}\right)$=4750 kg

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Q4 | Ex-8E |Class 7 |S.Chand | New Learning Composite maths |Percentage and Its Applications |Ch-7 |myhelper

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Question 4

A packet of cake mix has the composition of its contents shown on the label. Calculate the percentage composition of the cake mix.

Nutritional  value (per 50 g serve)
Protein	3.5 g
Fat	5.5 g
Carbohydrates	27 g
Other ingredients	14 g

Sol :

∴Percentage of protein$=\frac{3.5}{50} \times 100$=7% 

∴Percentage of fat$=\frac{5.5}{50} \times 100$=11% 

∴Percentage of carbohydrates$=\frac{27}{50} \times 100$=54% 

∴Percentage of other ingredients$=\frac{14}{50} \times 100$=28% 

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Q5 | Ex-8E |Class 7 |S.Chand | New Learning Composite maths |Percentage and Its Applications |Ch-7 |myhelper

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Question 5

The average composition (by weight) of milk is shown in the table.

Ingredients	Percentage
Carbohydrate	5
Protein	3
Fat	4
Water	87
Other	1

(a) How many grams are there of each component in 1 kg of milk?

Sol :

[1 kg=1000 gm]

∴Quantity of carbohydrates$=\left(1000 \times \frac{5}{100}\right)$=50 gm

∴Quantity of protein$=\left(1000\times \frac{3}{100}\right)$=30gm

∴Quantity of fat$=\left(1000 \times \frac{4}{100}\right)$=40 gm

∴Quantity of water$=\left(1000 \times \frac{87}{100}\right)$=870 gm

∴Quantity of other ingredient$=\left(1000 \times \frac{1}{100}\right)$=10 gm

(b) How many grams of proteins are there in 7.5 kg of milk?

Sol :

7.5 kg=7500 gm

∴Quantity of protein$=\left(7500\times \frac{3}{100}\right)$=225 gm