Class 8 Maths Chapter 8 Comparing Quantities

Class 8 Maths Chapter 8 Comparing Quantities

*YOUTUBE video of class 8 of whole syllabus

*YOUTUBE video of space and science knowledge

Class 8 Maths Chapter 9 Algebraic Expressions and Identities

Syllabus of Class 8 Mathematics

1.Rational Numbers

2.Linear Equations in one variable

3.Understanding Quadrilaterals

4.Practical Geometry

5.Data Handling

6.Squares Square Roots

7.Cube and Cube Roots

8.Comparing Quantities

9.Algebraic Expressions and Identities

10.Visualising Solid Shapes

11.Mensuration

12.Exponents and Powers

13.Direct and Inverse Properties

14.Factorisation

15.Introduction to Graph

16.Playing with Numbers

*Study Material for Class 8 Maths Chapter 8 Comparing Quantity

Introduction

•   S.P. is selling price

•   C.P. is cost price

•   The overhead expenses are a part of CP.

•   Profit or loss is always calculated on CP

•   For profit, SP>CP and for loss CP>SP

•   Discount is always calculated on the marked price.

•   VAT is not a part of selling price. Although it is calculated on the SP but it is excluded from the SP while calculating profit or loss.

•   Formula for compound interest gives

                            Amount=P(1+R/100)n

                                  then CI=A-P

•   If the interest is compounded half yearly the time period becomes twice as much as the numbers of years. The rate of interest is reduced to half.

•   We compare two quantites by division.It is called ratio. Quantities written in same unit. Ratio has no unit

•   Another way to compare quantity is to express in percentages.

•   Profit= Profit/CPX100, Loss= Loss/CpX100

Exercise 8.1

Question 1

(a) Speed of a cycle 15 km per hour to the speed of scooter 30 km per hour.

(b) 5 m to 10 km  (c) 50 paise to ₹ 5

Solution:

(a) Speed of a cycle 15 km per hour to the speed of scooter 30 km per hour

     Ratio = Speed of Cycle : Speed of Scooter

              = 15 km per hour : 30 km per hour

              = 15/30 = 1/2 

     So, the ratio is 1 : 2

(b) 5 m to 10 km

     First of all, the units of both quantities must be same 

     So, Convert 10 km into m

     Since 1 km = 1000 m

     Hence, 10 km = 10,000 m

     Ratio = 5 m : 10,000 m

              = 5/10000 = 1/2000

     So, the ratio is 1 : 2000

(c) 50 paise to ₹ 5

     First of all, the units of both quantities must be same 

     Convert ₹ 5 into paise

     Since ₹ 1 = 100 paise 

     Hence, ₹ 5 = 500 paise

     Ratio = 50 paise : 500 paise

              = 50/500 = 1/10

     So, the ratio is 1 : 10

Question 2: Convert the following ratios to percentages.

(a) 3 : 4   (b) 2 : 3

Solution:

In order to convert ratios to the percentage, we must multiply it with 100

(a) 3 : 4

     3 : 4 = (3/4) X 100 = 75%

(b) 2 : 3

     2 : 3 = (2/3) X 100 = 66.66% or 67% (approx)

Question 3: 72% of 25 students are good in mathematics. How many are not good in mathematics?

Solution:

Method 1:

Total students = 25

72% student are good in mathematics, converting it to numbers

Number of students good in mathematics = 72% of 25

                                                                    = (72/100) X 25

                                                                    = 18

So number of students who are not good in mathematics = 25 – 18 = 7

So, 7 students are there who don’t like mathematics.

Method 2:

It is given that 72% of 25 students are good in mathematics

So the percentage of people who are not good in mathematics 100% – 72% = 28%

Number of people who are not good in mathematics = 28% of 25 = (28/100) X 25 = 7

So, 7 students are there who don’t like mathematics.

Question 4: A football team won 10 matches out of the total number of matches they played. If their win percentage was 40, then how many matches did they play in all?

Solution:

Method 1:

Let us assume that the team played 100 matches and the winning percentage is 40

So, we can say the team won 40 matches out of 100

Also, they won 1 match out of 100/40 matches

Hence, 10 matches were won out of (100/40) X 10 = 25

So, the football team played 25 matches in all.

Method 2:

Let us assume the football team played a total of x matches 

The winning percentage is 40% and they won 10 matches

So, we can say

40% of x = 10

(40/100). x = 10

Hence, x = 25 

So, the football team played 25 matches in all.

Question 5: If Chameli had ₹ 600 left after spending 75% of her money, how much did she have in the beginning?

Solution:

Method 1:

Let us assume that Chameli had ₹ 100 in the beginning 

It is given that Chameli had spent 75% of her money 

So the money spent by her = 75% of 100 = (75/100) X 100 = ₹75

Hence, money left with her = ₹100 – ₹75 = ₹25

Now, 

₹25 are left if she had ₹100 in the beginning

₹1 is left if she had ₹(100/25)

So, ₹600 will be left if she had ₹(100/25) X 600 i.e ₹2400 in the beginning

Hence, Chameli had ₹2400 in the beginning.

Method 2:

Let us assume Chameli had ₹x in the beginning 

After spending 75% of x she had ₹ 600 left 

So, (100 – 75)% of x = ₹600

= >(25/100). x = 600

Hence, x = ₹2400

Hence, Chameli had ₹2400 in the beginning.

Question 6: If 60% of people in a city like a cricket, 30% like football, and the remaining like other games, then what percent of the people like other games? If the total number of people are 50 lakh, find the exact number who like each type of game.

Solution:

Total number of people = 50 lakh

60% of people like Cricket

So, the number of people like Cricket = 60% of 50,00,000

                                                             = (60/100) X 50,00,000 = 30,00,000

30% of people like Football

So, the number of people like Football = 30% of 50,00,000

                                                              = (30/100) X 50,00,000 = 15,00,000

Percentage of people like other games = (100% – 60% – 30%) = 10%

So, the number of people like other games = 10% of 50,00,000

                                                                      = (10/100) X 50,00,000 = 5,00,000

Hence, 30 lakh people like Cricket, 15 lakh people like Football and 5 lakh people like other games.

 

 

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