Ch 7 mathematics class 7 ratio and proportion

INTRODUCTION
There is a 20 over cricket match going on between
India and Zimbabwe. India scores 200 runs with Kohli
playing a good knock of 76* runs. Zimbabwe gets
bowled out at 100 runs. So India wins by a good
margin. That’s a qualitative definition. But by how
much did India win? This is answered by the concept
of ratios and proportions. So come, let us know more
about ratios and proportions.

GLOSSARY
 Ratio - the comparison or simplified form of two quantities of the same kind .
We make use of ratios to compare two things. The sign used to denote a ratio
is ‘:’.
 Proportion - When two ratios are equal in value, then they are said to be
in proportion. In simple words, it compares two ratios. Proportions are
denoted by the symbol ‘::’ or ‘=’.
Equivalent - two values, numbers or quantities which are the same
 STRENUOUS – DIFFICULT
 TRANQUIL-SIMPLE

Ratio
a: b ⇒ a/b
where a and b could be any two quantities.
Here, “a” is called the first term or antecedent, and “b” is called the second term
or consequent.
Example: In ratio 4:9, is represented by 4/9, where 4 is antecedent and 9 is
consequent.
If we multiply and divide each term of ratio by the same number (non-zero), it
doesn’t affect the ratio.
Example: 4:9 = 8:18 = 12:27

When we compare the relationship between two numbers dealing with a
kind, then we use the ratio formula.
It is denoted as a separation between the number with a
colon (:). Sometimes a division sign is also used to express ratios.
For example, we are making a cake, then the recipe sometimes says to
mix flour to water in the ratio 2 part
1. That means if you using 2 cups of flour then mix it with 1 cup of water.
Both the numbers should be non-zero in order to make a meaning out of
the comparison. Some ratios are
denoted in percentages and decimals as well.
The ratio formula is
a:b⇒ab

EQUIVALENT RATIOS
 Two ratios that have the same value are called equivalent ratios. To find an
equivalent ratio, multiply or divide both quantities by the same number. It is the
same process as finding equivalent fractions.
 The recipe uses 3 cups of flour and 1 cup of butter and she wants to make 3
batches of the recipe. To find how much flour and butter she needs, Angie can
use equivalent ratios. TELL HOW .
NOW LET’S CHECK THE ANSWER

ANSWER PLZZZZ..
 First, write a ratio for the number of cups of flour and the number of cups of butter.
3 cups of flour
-------------------
1 cups of butter
 Next, find an equivalent ratio by multiplying the numerator and denominator by 3.
3×3= 9
------- -----
1×3= 3
The equivalent ratio tells you that Angie will need 9 cups of flour and 3 cups of butter to make 3
batches of cookies.

STRENUOUS QUESTION WHICH WILL MAKE UR MIND
PUZZELED
John weights 65.7
kg. If he reduces
his weight in the
ratio
5 : 4, find his
reduced weight.

STRENUOUS QUESTION ANSWER
STEP-BY-STEP EXPLANATION
LET THE PREVIOUS WEIGHT BE 5X
5X = 65.7
X = 65.75
X = 13.14
THEREFORE, THE REDUCE WEIGHT = 4 × 13.14 = 52.56 KG

Proportion
• CONTINUED PROPORTION

 Proportion is equality of two ratios: e.g. a:b= c:d
 i.e. Ratio between first and second is equal to ratio between third and fourth
term.
 (ii) a and d are called extreme terms and band c are called mean terms and a xd =
bxc
 (iii) Fourth term is called fourth proportional.

Continued Proportion
Three quantities are called in continued proportion if
the ratio between first and second is equal to the ratio
between secondand third i. e.
a, b,c are in continued proportion if a : b = b:c
b the middle term is called the mean proportional
between a and c and the third term is called the third
proportional to a and b.

LET’S TEST
 Find p in each case so that the numbers are in continued proportion.
(i) p, 1 , 12, 2
____
2
(ii) 16, p, 9

UR RESULTS !!
(i)1
____
8
(ii) 12

Unitary Method
The unitary method is used to find the value of a
single unit from a given multiple. For example, the
price of 40 pens is Rs. 400, then how to find the value
of one pen here. It can be done using the unitary
method. Also, once we have found the value of a
single unit, then we can calculate the value of the
required units by multiplying the single value unit.

NOW LET’S START FROM ONE TRANQUIL QUESTION
12 farmers harvest the crops in the field in 20 hours.
How many workers will be required to do the same
work in 15 hours?

NOWSEETHEANSWER
12 farmers need 20 hours to complete the harvesting.
Find the number of farmers needed if the work is to be completed in 1 hour:
20 hours = 12 farmers
1 hour = 12 x 20 = 240 farmers
Find the number of farmers needed if the work is to be completed in 15 hour:
1 hour = 240 farmers15 hours = 240 ÷ 15 = 16 farmers
Answer: 16 farmers are needed to complete the work in 15 hours

SIMPLEST QUESTION
Fifteen post cards cost Rs. 2.25.
What will be the cost of 36 post
cards? How many postcards can we
buy in Rs. 45?

SOLUTION
15 Post cards = Rs 2.25
1 Post card = 2.25/15 = 0.15
Hence, 36 Post cards 0.15 x 36 = Rs 5.4
Let the no. of post cards bought in 45 rs be x
Therefore, 45/x 0.15
x = 45/0.15 = 300

EX-7.1 [ RESUME FROM EX-1.1 QUE-6]

BYE – BYE !!!!
Ok now I have to go . BYE!!
STRIVE DONE BY –
NANDINI
VII-B
ROLL NO. 33

Ch 7 mathematics class 7 ratio and proportion

Ch 7 mathematics class 7 ratio and proportion

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Ch 7 mathematics class 7 ratio and proportion