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

 Exercise 8F

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

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Question 1

55 per cent of the students in a school are girls. What percentage of the students are boys? Find the number of students, if there are 216 boys.

Sol :

∴Percentage of boys=100-55=45%

45% of student=216

1% of student$=\frac{216}{45}$

45% of student$=\frac{216 \times 100}{45}$=480

∴Total number of student=480

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

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Question 2

If 10% is deducted from a bill, Rs. 7200 remains to be paid. How much is the bill?

Sol :

∴Remaining bill=(100-10)=90%

90% bill=7200

1% bill $=\frac{7200}{90}$

100% bill $=\frac{7200 \times 100}{90}$=8000

∴Total bill=8000

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

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Question 3

Calculation gives the length of a line segment as 6.4 cm, while from drawing and measurement it is obtained as 6.6 cm. Find the error per cent.

Sol :

∴Error length=(6.6-6.4)=0.2 cm

In 6.4 cm the error is 0.2 cm

In 1 cm the error is $=\frac{0.2}{6.4}$ cm

In 100 cm the error is $=\frac{0.2\times 100}{6.4}=\frac{25}{8}=3\frac{1}{8}$ cm

∴Error Percentage is $3\frac{1}{8}$%

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

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Question 4

Atul deposited 30% of his income in a bank. After spending 50% of the remaining, he had Rs. 10,500 left with him. What is his income?

Sol :

Remaining income after depositing in bank=100-30=70%

50% of 70%=35%

35% of income is 10500

1% of income is $\frac{10500}{35}$

100% of income is $=\frac{10500 \times 100}{35}$=30000

∴Atul's income is 30000

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

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Question 5

Manish obtained 498 marks out of 600 marks and Aravind scored 640 marks out of 800 marks. Whose performance is better?

Sol :

∴Percentage of Manish score$=\left(\frac{498}{600} \times 100\right)$=83 %

∴Percentage of Arvind's score$=\left(\frac{640}{800}\times 100\right)$=80%

Ans : Manish's performance is better than Arvind performance

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Q6 | Ex-8F |Class 7 |S.Chand | New Learning Composite maths |Percentage and Its Applications |Ch-7 |myhelper

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Question 6

In a graduate class of 200, 40% are women and 1/5 becomes lecturers. If the number of men who became lecturers is twice that of women, calculate approximate percentage of men who became lecturers.

Sol :

Number of women$=\frac{40}{100}\times 200$=80

Number of women who become lecturer$=80\times \frac{1}{5}$=16

Number of men who becomes lecturer=16×2=32

Number of men=200-80=120

∴Percentage of men who becomes lecturer$=\left(\frac{32}{120}\times 100\right)$

=26.6%

≃27%

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Q7 | Ex-8F |Class 7 |S.Chand | New Learning Composite maths |Percentage and Its Applications |Ch-7 |myhelper

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Question 7

The price of an article is reduced by 25%. In order to retain the original price, by what percentage should the present price be increased?

Sol :

Let the price 100

25% reduced new price 75

So the price raised should be $=\left(\frac{25}{75}\times 100\right)$=33.33%

Ans : The present price increased 33.33%

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Q8 | Ex-8F |Class 7 |S.Chand | New Learning Composite maths |Percentage and Its Applications |Ch-7 |myhelper

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Question 8

In a mixture of milk and water, the proportion of water by weight is 75%. If in the 60 g mixture, 15 g of water is added, what would be the percentage of water?

Sol :

In 60 g mixture , weight of water$=\left(\frac{75}{100}\times 60\right)$=45 gm

15 g water is added , now weight of water=45+15=60gm

Now , Percentage of water $=\left(\frac{60}{75}\times 100\right)$=80%

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Q9 | Ex-8F |Class 7 |S.Chand | New Learning Composite maths |Percentage and Its Applications |Ch-7 |myhelper

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Question 9

One litre of water is evaporated from a 6 litre solution containing 4% sugar. Find the percentage of sugar in the remaining solution.

Sol :

Quality of sugar in 6 litre solution $=\left(\frac{4}{100}\times 6\right)$=0.24 litre

1 litre of water evaporated from a 6 litre solution

Now, quantity of solution=(6-1)=5 litres

Percentage of sugar in remaining solution$=\left(\frac{0.25}{5}\times 100\right)$=4.8%

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Q10 | Ex-8F |Class 7 |S.Chand | New Learning Composite maths |Percentage and Its Applications |Ch-7 |myhelper

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Question 10

State Electricity Board gives 15% discount on electricity bills, if it is paid before due date. A person gets Rs. 54 as discount. What was the actual amount of the bill?

Sol :

State Electricity Board gives 15 Rs discount on 100

State Electricity Board gives 1 Rs discount on $=\frac{100}{15}$

State Electricity Board gives 54 Rs discount on $=\frac{100\times 54}{15}$=360

Ans : Actual deposit of bill is 360