### NCERT Solutions For Class 7 Maths Chapter 8 Exercises

- NCERT Solutions For Class 7 Maths Chapter 8 Comparing Quantities Exercise 8.1
- NCERT Solutions For Class 7 Maths Chapter 8 Comparing Quantities Exercise 8.2
- NCERT Solutions For Class 7 Maths Chapter 8 Comparing Quantities Exercise 8.3

*EXERCISE- 8.1:*

*QUESTION 1:*

*Calculate the ratio:*

* (i) Rs10 to 50 paise (ii) 10kg to 500g*

* (iii) 60m to 20cm (iv) 20days to 50 hours*

*Solution; *

*(i) Rs.10 to 50 paise*

=> 10 x 100 = 1000 paise (Since , Rs.1 = 100 paise)

Thus, the ratio = 1000/50 = 20 : 1

*(ii) 10kg to 500g*

10 x 1000= 10000g (Since 1kg is 1000g)

Thus, the ratio = 10000/500 = 20 : 1

*(iii) 60m to 20cm*

60 x 100 = 6000cm (Since 1m = 100cm)

Thus, the ratio =6000/20 = 300 : 1

*(iv) 20days to 50 hours*

20 x 24 = 480 hours

Thus, the ratio = 480/50 = 48 : 5

*QUESTION 2:*

*A computer lab has 2 computers for every 4 students. For 20 students how many computers will be required?*

*Solution;*

Given,

4 students = 2 computers

1 student requires = 2/4 computers.

Therefore, 20 students require = (2/4) x 20 = 10 computers.

*QUESTION 3:*

*Mizoram has a population of 10 lakh and Sikkim has a population of 6 lakh. Area of Mizoram is 21,000 km ^{2} and the area of Sikkim is 7000 km^{2}.*

* (i) Find the number of people per km ^{2} in both the states.*

* (ii) Which state has a lesser population?*

*Solution;*

** (i)** People per km

^{2}= Population/ Area

In Mizoram = 1000000/21000 = 47.61 ≃48 people/km^{2}

In Sikkim = 600000/7000 = 85.71 ≃ 86 people/km^{2}

** (ii)** Sikkim has a lesser population.

* *

*EXERCISE- 8.2*

*QUESTION 1:*

*Convert the given fractional numbers to percent:*

*(a) 1/3 (b)6/5 (c)4/25 (d)3/7*

*Solution;*

** (a)** 1/3 = (1/3) x 100% = 100/3 = 33.33%

** (b)** 6/5 = (6/5) x 100% = 6 x 20 = 120%

** (c)** 4/25 = (4/25) x 100% = 16%

** (d)** 2/7 = (2/7) x 100% = 28.57%

* *

*QUESTION 2:*

*Express the given decimal numbers in percentages.*

*(a) 0.31 (b)0.03 (c)19.62 (d)0.007*

*Solutions;*

** (a)** 0.31 = (31/100) x 100% = 31%

** (b)** 0.03 = (3/100) x 100% = 3%

** (c)** 19.62 = (1962/100) x 100% = 1962%

** (d)** 0.007 = (7/1000) x 100% = 0.7%

* QUESTION 3:*

*Find what part of the following figures is colored; also find the percentage of the colored part.*

*Solutions;*

** (i)** Colored part = 1/4

Therefore, percentage of the colored portion = (1/4) x 100% = 25%

** (ii)** Colored portion = 3/5

Therefore, percentage of the colored portion = (3/5) x 100 =60%

** (iii)** Colored portion = (3/8) x 100% = 37.5%

*QUESTION 4:*

** Calculate** :

*(a) 15% of 450 (b) 2% of 2 hour*

* (c) 10% of ₹2600 (d) 50% of 5 kg*

*Solutions;*

** (a)** 15% of 450 = (15/100) x 450 = 67.5

** (b)** 2% of 2 hours= 2% of (2×3600) secs (Since 1 hour = 60 x 60 secs)

= (2/100) x 7200 =144secs.

** (c)** 10% of Rs.2600 = (10/100) x 2600

=Rs.260

** (d)** 50% of 5kg = 50% of (5000g) (Since 1kg = 1000g)

= (50/100) x 5000

= 2500 g or 2.5kg

* *

* QUESTION 5:*

*Calculate the total quantity if:*

* (a) 5% of it is 100 *

*(b) 10% of it is ₹1060*

*(c) 20% of it is 800 km*

*(d) 90% of it is 18 minutes*

*(e) 9% of it is 60 liters*

*Solutions;*

let the total quantity be Y in all above cases,

** (a)**5% of Y = 100

=> (5/100) x Y =100

=> Y=(100×100)/5 =2000

** (b)**10% of Y = 1060

=> (10/100) x Y = 1060

=> Y = (1060 x 100)/10 = Rs.10600

** (c)**20% of Y = 800

=> (20/100) x Y = 800

=> Y = (800 x 100)/20 = 4000km

** (d)** 90% of Y = 18min

=> (90/100) x Y = 18

=> Y=(18 x 100)/90 =20mins.

** (e)** 9% of Y = 60

=> (9/100) x Y = 60

=> Y = (60 x 100)/9 =666.66liters.

*QUESTION 6:*

*Convert the following percentages to fractions , simplest fractions and decimal numbers:*

*(a)20% (b)25% (c)5% (d)120%*

*Solution;*

Percentage |
Fractions |
Simplest Fraction |
Decimal Numbers. |

20% | 20/100 | 1/5 | 0.2 |

25% | 25/100 | 1/4 | 0.25 |

5% | 5/100 | 1/20 | 0.05 |

120% | 120/100 | 6/5 | 1.2 |

*QUESTION 7: *

*12000 voters constituted a constituency, out of which 80% voted. What percentage and number of voters did not vote?*

*Solution;*

Given,

Total no. of voters = 12000

Percentage who voted = 80%

Thus, percentage who did not vote = 100 -80 = 20%

Therefore, the number of people who did not vote = 20% of 12000

= (20/100) x 12000 = 2400

*QUESTION 8: *

*Sanjay saves Rs.5000 every month, if this is 20% of his salary. What is his monthly salary?*

*Solution;*

Let Sanjay’s salary be Y

Now, 20% of Y = 5000

(20/100) x Y = 5000

Y = Rs.25000

Therefore,Sanjay’s salary is Rs.25000

*QUESTION 9: *

*A local**dota team played 10 matches in a season. If they won 40% of their matches, in how many matches do they win?*

*Solution;*

Given,

Number of matches played by the dota2 team =10

Percentage of matches won = 40%

Therefore, total matches they were victorious in = 40% of 10

= (40/100) x 10

=4.

*EXERCISE- 8.3*

** QUESTION 1**:

*What is the profit and theloss for the following transaction.Also find what is the profit percentage and the loss percentage in the cases given:*

*(i) Gardening shears were bought for Rs 250 and were sold for Rs 325*

*(ii) A refrigerator was bought for Rs 12,000 and sold for Rs 13,500*

*(iii) A cupboard was bought for Rs 2,500 and sold for Rs 3,000.*

*(iv) A shirt was bought for Rs 250 and sold for Rs 150*

*Solution;*

** (i)**the cost price of the gardening shears: Rs 250

The selling price of the gardening shears: Rs 325

Since, SP> CP therefore here it is a profit.

Therefore profit = SP – CP = Rs 325 – Rs 250

= Rs 75

Now profit % =

=

Therefore, Profit = Rs 75 and Profit % = 30%

** (ii)** Cost prince of refrigerator = Rs 12,000

Selling price of Refrigerator = Rs 13,500

Since, S.P > C.P Therefore, it is a profit.

Therefore, Profit = SP – CP = Rs 13500 – Rs 12000 = Rs 1500

Now profit % =

=

Therefore, Profit = Rs 1,500 and Profit % = 12.5 %

** (iii)** Cost price of cupboard = Rs 2500

Selling price of cupboard = Rs 3,000

Since, SP> CP, Therefore it is a profit.

Profit = SP – CP = Rs 3,000 – Rs 2,500 = Rs 500

=

Therefore, Profit = 500 and profit % = 20%

** (iv)** Cost price of shirt = Rs 250

Selling price of shirt = Rs 150

Since CP > SP, therefore here it is a loss.

Therefore Loss = CP – SP = Rs 250 – Rs 150

= Rs 100

Now loss % =

=

Therefore , Loss = Rs 100 and Loss% = 40%

*QUESTION 2: *

*Convert the following ratio to its percentages:*

*(i) 3 : 1*

*(ii) 2 : 3 : 5*

*(iii) 1 : 4*

*(iv) 1 : 2 : 5*

*Solution;*

** (i)**3 : 1

Total part = 3 + 1 = 4

Therefore, Fractional part =

=> Percentage of parts =

=> Percentage of parts = 75 % : 25 %

** (ii)**2 : 3 : 5

Total part = 2 + 3 + 5 = 10

Therefore, Fractional part =

=> Percentage of parts =

=> Percentage of parts = 20 % : 30 % : 50 %

** (iii)**1 : 4

Total part = 1 + 4 = 5

Therefore, Fractional part =

=> Percentage of parts =

=> Percentage of parts = 20% : 80%

** (iv)**1 : 2 : 5

Total part = 1 + 2 + 5 = 8

Therefore, Fractional part =

=> Percentage of parts =

=> Percentage of parts = 12.5 % : 25 % : 62.5 %

*QUESTION 3: *

*The population of a city decreased from 25,000 to 24,500. Find the decrease in percentage.*

*Solution;*

The decrease in population of a city is from 25,000 to 24,500.

Population Decreased = 25000 – 24500 = 500

Decreased percentage =

=

Hence, the percentage of decrease in the population is 2 %.

** QUESTION 4**:

*Reah and Reuben** bought a caravan for Rs. 3,50,000. The next year, the price raised to Rs 3,70,000. What is the percentage of price increased?*

*Solution;*

Increased in price of the caravan from Rs 3, 50,000 to 3, 70,000

Amount change = Rs 3, 70,000 – Rs 3, 50,000 = Rs 20,000

Therefore, Increased percentage =

Hence, The percentage of price increased is

*QUESTION 5: *

*Harismitha** bought a T.V for Rs 10,000 and sold it at a profit of 20%. How much money did she get for it?*

*Solution;*

The cost price of T.V = Rs 10000

Profit percent = 20%

Now, Profit = Profit % of CP

=

= Rs 2000

Selling price = CP + Profit = Rs 10000 + Rs 2000 = Rs 12000

She gets Rs 12000 on selling the T.V

*QUESTION 6: *

*Nancy sold a washing machine for Rs 13500. She Lost 20% in the bargain. What is the price that she bought the washing machine for?*

*Solution;*

Selling price of washing machine= Rs 13,500

Loss percent = 20%

Let the cost price of washing machine be Rs x

Since, Loss = Loss % of CP

=> Loss = 20 % of Rs x =

Therefore, SP = CP – Loss

Hence, The cost price of washing machine is Rs 16,875.

*QUESTION 7: *

*(a) Chalk contains Calcium, Carbon and Oxygen in the ratio 10: 3 : 12. Find the percentage of carbon in chalk.*

*(b) If in a stick of chalk, Carbon is 3g, what is the weight of the chalk stick?*

*Solution;*

** (a)** Given ratio = 10 : 3 : 12

Total part = 10 + 3 + 12 = 25

Part of carbon =

Percentage of Carbon part in Chalk =

** (b)** Quality of Carbon in chalk stick = 3g

Let the weight of chalk be x g.

Then, 12 % of x = 3

=>

=> x =

Hence, the weight of chalk stick is 25g.

*QUESTION 8: *

*Amulya buys a book for Rs 275 and sells it at a loss of 15% . How much does she sell it for?*

*Solution;*

The cost of a book = Rs 275

Loss percentage = 15 %

Loss = Loss % of CP = 15 % of 275

=

Therefore , SP = CP – Loss = 275 – 41.25 = Rs 233.75

Hence, Amulya sold the book for Rs 233.75

*QUESTION 9: *

*Find the amount to be paid at the end of 3 years in the following cases:*

*(i ) Principal = Rs 1200 at 12 % p. a*

*(ii) Principal = Rs 7500 at 5 % p. a*

*Solution;*

** (i)** Here, Principal (p) = 1200

Rate ( r ) = 12 % p a

Time ( T ) = 3 years

=432

Now, Amount = Principal + Simple Interest

= Rs 1200 + Rs 432

= Rs 1632

** (ii)** Here, Principal (p) = 7500

Rate ( r ) = 5 % p a

Time ( T ) = 3 years

= 1125

Now, Amount = Principal + Simple Interest

= Rs 7500 + Rs 1125

= Rs 8625

*QUESTION 10: *

*What rate gives Rs 280 as interest on a sum onRs 56,000 in 2 years?*

*Solution;*

Here, Principal (P ) = Rs 56000

Simple Interest (SI ) = Rs 280

Time ( T) = 2 yrs

Simple interest =

=> 280 =

=> R =

=> Hence, the rate of interest on sum is 0.25%

*QUESTION 11: *

*If Deepak gives an interest of Rs 45 for one year at 9% rate per annum. What is the sum he has borrowed from Nancy?*

*Solution;*

Simple Interest = Rs 45

Rate (R ) = 9%

Time ( T) = 1 year

Simple interest =

=> 45 =

=> P =

=> P = Rs 500

Hence, she had borrowed Rs 500.