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1. Percentage - 2

2. change = 100
error = 100
• A = x % of B => if B = 100 then A = x
• A = x % more than B => if B = 100 then A = 100 + x
• A = x % less than B => if B = 100 then A = 100 – x
• 100 % of any value is value itself.
Basics :
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3. 1. A man is saving 33 of his income. If his income is increased by 25% and
expenditure is increased by 40%, then what is the % change in his savings?
2. A student by mistake multiplied a number with instead of multiplying with .
What is the % error in calculation?
3. The population of a town is increasing by 20% every year. If the present
population of town is 72000, then what is the population of the town 2 years ago
?
4. The price of the sugar is decreased by 30%. What is the % change in
expenditure if consumption is increased by 40% ?
5. In an examination, A boy scores 31% of max marks and fails by 12 marks. A girl
scores 45%of max marks and pass by 16 marks. Find the max marks and the
% required to pass?
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4. 1. A man is saving 25% of his income. If his income is increased by 20%
and expenditure is increased by 10%, then what is the % change in
his savings?
Ans :
income = savings + expenditure
100 25 75
120 37.5 82.5
% change = 100
= 50%
100 % = 75
10% = 7.5
% change in his savings = 50%
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5. A student by mistake multiplied a number with instead of
multiplying with . What is the % error in calculation?
2.
Let take a number which is multiplied by both numbers
i.e. the lcm of two denominators. => lcm of (4,5) = 20
=> % error = 100
= 36%
% error = 100
= 36%
Ans : 20 = 16
20 = 25
25 --- 16
100 --- 64
36%
% error in calculation = 36% COMSCIGUIDE

6. A student by mistake divided a number with instead of
multiplying with 2. What is the % error in calculation?
2.
First convert both operations into one format ,the
operation that we have to do on the number. Here it is
multiplication.
=> % error = 100
= 75%
% error = 100
= 75%
Ans :
4 --- 1
100 --- 25
75%
% error in calculation = 75% COMSCIGUIDE

7. The population of a town is increasing by 20% every year. If the
present population of town is 72000, then what is the population of
the town 2 years ago ?
3.
The population of the town is increasing every year. Before 2
years it is less than the present population.
 the percentage improvement is 20 %
i.e one year later it will be present population
Similarly the population after 2 years will be present population
Therefore 2 years ago the population will be present population
Population 2 years ago = 72000 = 50,000
Ans :
Population of the town 2 years ago = 50,000COMSCIGUIDE

8. The price of the sugar is decreased by 30%. What is the % change in
expenditure if consumption is increased by 40% ?
4.
Expenditure = consumption price
10000 100 100
9800 140 70
Ans :
100 = 2%
Method - 2
Method - 1
100 140 98
2% decrease
40 42
For method -2 assume initial amount as 100
% change in expenditure = 2%
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9. In an examination, A boy scores 31% of max marks and fails by 12
marks. A girl scores 45%of max marks and pass by 16 marks. Find the
max marks and the % required to pass?
5.
Ans :
Maximum marks = 200
% Required to pass = 37%
Max marks boys girls
100 31 45
 14% = 28 marks
 1% = 2 marks
 100% = 200 marks = maximum marks
 12 marks = 6% and already boy has 31%
 31+6 = 37%
%required to pass is 37
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Problems for practice are given in the description of the video.
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11. Practice problems
on Percentages

12. 1. A train crosses a pole in 12 sec. It crosses a bridge of length 300m in 27
sec. what is the time taken by the train to cross a bridge of length of 600m?
2. A train crosses a bridge of length 122m in 17 sec. it crossed another bridge
of length 210m in 25 sec. find the length of the train?
3. A train travelling at a speed of 54kmph crosses a platform in 36 sec and a
man standing on the platform in 20 sec. find the length of the platform?
4. A train of length 240m travelling at a speed of 64kmph overtakes a man
running at a speed of 10 kmph in __ sec ?
5. A train starts from a station X at 6am and reaches another station Y at 10
am. Another train starts from station Y at 8am and reaches station ‘X’ at
11:30am. At what time do the trains cross each other?
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13. The price of the sugar is increased by 25%. What is the % change in
consumption, if expenditure is increased by 50% ?
4.
Ans :
100 125 150
50% increase
25% x%
For method -2 assume initial amount as 100
100 = 20%
% change in consumption = 20%
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14. The value of a machine is decreases by 30% every year. If the
present value of a machine is 1,47,000, then what is the value of the
machine 2 years ago?
3.
The value of a machine before 2 years will be present price
Value of a machine 2 years ago = 1,47,000 = 3,00,000
Ans :
Value of the machine 2 years ago = 3,00,000
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15. A student by mistake multiplied a number with instead of
dividing with 3. What is the % error in calculation?
2.
First convert both operations into one format ,the
operation that we have to do on the number. Here it is
multiplication.
=>
% error = 100
= -800%
Ans :
9 --- 1
900 --- 100
-800% error in calculation = 800%
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16. A student by mistake multiplied a number with instead of dividing
with . What is the % error in calculation?
2.
 Error in calculation is zero
 Since multiplying with 2/5 is equal to dividing with 5/2
Ans :
% error in calculation = 0%
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17. Subscribe to :
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