CBSE Notes Class 7 Maths Chapter 7 - Comparing Quantities
Comparing Quantities involves using ratios, percentages, and proportions to compare two or more values. A ratio shows how many times one value contains another, while percentages express a value as a fraction of 100. Proportion compares two equal ratios. Concepts like profit, loss, and simple interest help in comparing financial quantities effectively.
1.0Download CBSE Class 7 Maths Chapter 7 Comparing Quantities Notes : Free PDF
Download CBSE Class 7 Maths Chapter 7 – Comparing Quantities Notes in a free and easy-to-access PDF format. These notes provide a clear summary of key concepts such as percentages, profit and loss, simple interest, and ratio and proportion.Strengthen your understanding of CBSE Class 7 Maths topics with well-organized content designed to support effective learning. Get your free PDF now!
2.0Comparing Quantities: An Introduction
To compare two quantities, ensure both quantities are expressed in the same units. Here are some examples:
- Joe’s height is 150 cm, while Tom’s height is 100 cm. The ratio of Joe's height to Tom's is:
Ratio =100150=23 or 3:2
- The ratio of 3 km to 30 m is:
30 m3 km=30 m3000 m=100:1
3.0Ratios
A ratio compares two quantities by showing how many times one value contains or is contained within the other. For instance, if there are 4 girls and 7 boys in a class, the ratio of girls to boys is 4:7.
Equivalent Ratios:
Multiplying both the numerator and denominator of a ratio by the same non-zero number gives an equivalent ratio. For example:
32 and 64 are equivalent ratios.
4.0Proportions
When two ratios are equal, they are said to be in proportion. This can be represented as either "::" or "=". For example:
2:3::6:9 or 32=96.
Also Read: Ratio and Proportion
5.0Calculating Percentage Increase or Decrease
To find the percentage change, use the following formula:
Percentage Change = Original Value Change in Value ×100
For example, if the price of a book increases from ₹20 to ₹25, the percentage increase is:
Change = 25 – 20 = 5,
Percentage Increase =205×100=25%
6.0Percentages
Percentages represent a ratio as a fraction of 100. For example:
40%=10040,25%=10025
If the denominator is not 100, convert the fraction to one that has a denominator of 100. For example:
53=10060=60%
7.0Converting Between Decimals, Fractions, and Percentages
- To change a decimal into a percentage, multiply the by 100. For example, 0.44 becomes 44%.
- To convert a fraction to a percentage, first make its denominator 100 and then express it as a percentage.
8.0Estimation and Interpretation Using Percentages
Percentages help interpret data more effectively. For example, if 60% of 200 chocolates were given to Joe and 40% to Tom:
Joe’s share =10060×200=120 chocolates, Tom’s share =10040×200=80 chocolates.
Ratios can also be expressed as percentages to enhance understanding of certain situations.
- Profit Percentage:
Profit Percentage is the percentage of profit made on the cost price of an item. It is calculated using the formula:
Profit Percentage =( Cost Price Profit )×100
Since Profit = Selling Price – Cost Price, we can express the formula as:
Profit Percentage =(CPSP−CP)×100
This formula helps to determine the percentage of gain in relation to the original cost price.
- Loss Percentage
Loss Percentage is the percentage of loss incurred on the cost price of an item. It is calculated using the formula:
Loss Percentage =( Cost Price Loss )×100
Since Loss = Cost Price – Selling Price, the formula becomes:
Loss Percentage =(CPCP−SP)×100
This gives the percentage of loss relative to the cost price.
9.0Prices Related to Buying and Selling
When discussing prices of items, there are two key terms:
- Selling Price (SP): This is the price at which an item is sold to a buyer.
- Cost Price (CP): This represents the original price at which an item was purchased.
To calculate the profit or loss made from a sale:
- Profit = Selling Price – Cost Price (when SP > CP).
- Loss = Cost Price – Selling Price (when CP > SP).
If SP is equal to CP, there is neither a profit nor a loss.
10.0Simple and Compound Interest
- The principal (P) is the initial sum borrowed.
- Interest is the extra amount paid to the lender.
- The total amount to be repaid (A) is: Amount = Principal + Interest.
- Simple Interest (SI) is calculated using:
SI=100P×R×T
where P is the principal, R is the rate of interest, and T is the time in years.
For example, if P = ₹200, R = 10%, and T = 3 years:
S I =100200×10×3 = ₹60.
Thus, the total amount to be paid is:
Amount = Principal + Simple Interest
= 200 + 60 = ₹260.
11.0Solved Examples on Comparing Quantities
Example 1: Compare 3 kilometers and 200 meters using ratios.
Solution:
First, convert kilometers to meters.
3 km = 3000 meters.
Now, the ratio is:
2003000=15:1
Thus, the ratio of 3 km to 200 m is 15:1.
Example 2: Convert the fraction 43 into a percentage.
Solution:
To convert a fraction to a percentage, multiply it by 100:
43×100=75%
Thus, 43 as a percentage is 75%.
Example 3: Find 20% of 250.
Solution:
To find 20% of 250, use the formula:
Percentage of a number =100 percentage × number
20% of 250=10020×250=50
Thus, 20% of 250 is 50.
Example 4: A shopkeeper buys a toy for ₹400 and sells it for ₹500. What is the profit percentage?
Solution:
First, calculate the profit:
Profit = Selling Price – Cost Price
= ₹ 500 – ₹ 400 = ₹100.
Now, calculate the profit percentage:
Profit Percentage =( Cost Price Profit )×100=(400100)×100=25%.
Thus, the profit percentage is 25%.
Example 5: A person buys a book for ₹250 and sells it for ₹200. What is the loss percentage?
Solution:
First, calculate the loss:
Loss = Cost Price – Selling Price
= ₹ 250 – ₹200 = ₹50.
Now, calculate the loss percentage:
Loss Percentage =( Cost Price Loss )×100=(25050)×100=20%.
Thus, the loss percentage is 20%.
Example 6: The ratio of girls to boys in a class is 3:5. Find the percentage of girls and boys in the class.
Solution:
Total parts = 3 + 5 = 8.
Percentage of girls:
83×100=37.5%
Percentage of boys:
85×100=62.5%
Thus, 37.5% of the class are girls and 62.5% are boys.
Example 7: If 6 : 8 :: x : 12, find the value of x.
Solution:
Set up the proportion:
86=12x
Cross-multiply:
6×12=8×x.
Simplifying:
72=8x⇒x=872=9
Thus, x = 9.
Example 8: Convert 0.75 into a percentage.
Solution:
To convert a decimal to a percentage, multiply it by 100:
0.75×100=75%
Thus, 0.75 as a percentage is 75%.
12.0Practice Questions on Comparing Quantities
- Convert the Following Fractions into Percentages:
- Find the Ratio of the Following Quantities in Same Units:
- 5 kg to 200 g
- 6 hours to 90 minutes
- ₹500 to ₹2000
- Percentage of a Number:
- Find 15% of 300.
- Find 45% of 800.
- A shopkeeper buys a mobile phone for ₹15,000 and sells it for ₹18,000. Find the profit percentage.
- If a car is bought for ₹3,00,000 and sold for ₹2,70,000, find the loss percentage.
- In a school, 65% of the students are boys. If the total number of students is 600, how many boys are there in the school? Convert it into percentage.
- The ratio of green balls to blue balls in a box is 4:6. What percentage of balls are green and what percentage are blue?
13.0Sample Questions on Comparing Quantities
- How Do We Find the Percentage of a Given Quantity?
Ans: To find the percentage of a quantity, multiply the given quantity by the percentage value and divide it by 100.
Formula:
Percentage of a quantity =100 Percentage value × Quantity
- How Do We Convert a Fraction to a Percentage?
Ans: To convert a fraction into a percentage, multiply the fraction by 100.
Formula:
Percentage = Denominator Numerator ×100
- What is the Formula for Simple Interest?
Ans: The formula for Simple Interest (SI) is:
SI=100P×R×T
where:
P = Principal (initial amount)
R = Rate of interest
T = Time (in years)
14.0Key Features of Class 7 Maths Chapter 7 - Comparing Quantities
- Clear formulas and methods to calculate profit, loss, and discount in commercial transactions.
- Step-by-step explanation of how to calculate simple interest with real-world examples.
- Summarized key points and formulas at the end of the chapter for fast and effective revision.
- Understanding how percentages are used to compare quantities and solve problems.
- Detailed coverage of ratios, proportions, and their applications in solving various problems.