FACTS  AND  FORMULAE  FOR  PERCENTAGE  QUESTIONS

 

 

I.Concept of Percentage : By a certain percent , we mean that many hundredths. Thus x percent means x hundredths, written as x%.

To express x% as a fraction : We have , x% = x/100.

Thus, 20% = 20/100 = 1/5;     

48% = 48/100 = 12/25, etc.

To express a/b as a percent : We have, ab=ab×100% .

 

Thus, 14=14×100%=25%

   

 

II. If the price of a commodity increases by R%, then the reduction in consumption so as not to increase the expenditure is R100+R×100%

If the price of the commodity decreases by R%,then the increase in consumption so as to decrease the expenditure is R100-R×100%

 

 

III. Results on Population : Let the population of the town be P now and suppose it increases at the rate of R% per annum, then :

1. Population after n years = P1+R100n

 

2. Population n years ago =  P1+R100n

 

 

IV. Results on Depreciation : Let the present value of a machine be P. Suppose it depreciates at the rate R% per annum. Then,

1. Value of the machine after n years = P1-R100n

 

2. Value of the machine n years ago = P1-R100n

 

 

V. If A is R% more than B, then B is less than A by

R100+R×100%    

If A is R% less than B , then B is more than A by 

R100-R×100%  

Q:

At an examination in which maximum marks are 500. K got 10% less than L, L got 25% more than M and M got 20% less than N. If K got 360 marks what percentage of marks was obtained by N ?

A) 80 B) 87
C) 78 D) 76
 
Answer & Explanation Answer: A) 80

Explanation:

Let marks obtained by N = x

M's marks = 0.80x

L's marks = 1.25 (0.80x)

K's marks = (0.90) (1.25) (0.80x)

= 0.9x

But 0.9x = 360 ⇒ x = 400

Percentage of Marks obtained by N

= 400 x 100/500 = 80%

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7 6277
Q:

Prashanth sold a album for $ 735 and made a profit of 22.5% . The cost price of the album went up by $120 and so Prashanth increased the selling price by $120. What is his profit % now ?

A) 19.32 % B) 18.75 %
C) 21.41 % D) 22 %
 
Answer & Explanation Answer: B) 18.75 %

Explanation:

Prashanth sold a album for $ 735 and made a profit of 22.5% .
CP = 735 x 100/122.5 = Rs. 600
New CP = 600 + 120 = Rs. 720
New SP = 735 + 120 = Rs. 855.

Profit = Rs. 135.

profit % = 100 x 135/720 = 18.75%.

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2 6252
Q:

A man spend 20% of his monthly salary on his children's education and 50% of his salary on food and transport. After Paying the rent of Rs.1000, he is left with Rs.2000. What is his monthly salary?

A) 7000 B) 10000
C) 14000 D) 20000
 
Answer & Explanation Answer: B) 10000

Explanation:

Let his monthly salary be 'P'

20% on children's education = 20P100 = P5

50% on food and transport = 50P100 = P2

1000 on rent

=> P - P5 - P2 - 1000 = 2000=> 3P = 30000=> P = 10000

 

Therefore, his monthly salary = Rs. 10,000

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4 6205
Q:

The price of an item is decreased by 25%. What percent increase must be done in new price to get the original price?

A) 33.33% B) 43.3%
C) 50% D) 55.3%
 
Answer & Explanation Answer: A) 33.33%

Explanation:

Let the price of an item be 100After 25% decrease, price of item = 75Increase in price to get the original price = 100-75 = 25% increase to get the original price = 25/75 X 100 = 100/3 = 33.33%

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Q:

Which value is equal to 5% of 1,500?

A) 35 B) 55
C) 75 D) 45
 
Answer & Explanation Answer: C) 75

Explanation:

In the question it is asked for 5% of 1500

5 x 1500/100 = 15 x 5 = 75.

 

Hence, 5% of 1,500 is equal to 75.

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10 6124
Q:

In a school of 1500 boys, 35% are Hindu, 30% are Sikh,15% are Muslims and remainning are Christians. Find number of christian boys in the school ?

Answer

Given total number of boys in the school = 1500


In that 35% are Hindu, 30% are Sikh, 15% are Muslims


=> 35 + 30 + 15 = 80%


Remaining Boys = 100% - 80% = 20% of 1500


=> 20 x 1500/100 = 300 boys are Christians. 

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5 6101
Q:

P, Q and R secured 45%, 50% and 60% marks respectively in Biology. M’s marks in Biology is 12.5 more than P’s marks and 4 less than R’s marks. Find out the individual marks of four students.

 

A. For the students, total marks obtained for Biology is 311.5.
B. Total of M’s and P’s marks in Biology is 147.5.
C. R has obtained 84 marks.

A) Only C B) Only A & B
C) All are required D) None of the statements is required
 
Answer & Explanation Answer: D) None of the statements is required

Explanation:

From the given data,
(60 - 45)% = 12.5 + 4
15% = 16.5
=> 100% = ?
100% = 16.5 x 100/15 = 110

Hence, P = 45% of 110 = 45x110/100 = 49.5
Q = 50% of 110 = 55
R = 60% of 110 = 60 x 110/100 = 66
M = 12.5 + 49.5 = 62 or 66 - 4 = 62

 

Hence, no statement is required to answer.

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3 5985
Q:

If three eighth of a number is 141. What will be the approximately value of 32.08% of this number ?

A) 101 B) 112
C) 104 D) 120
 
Answer & Explanation Answer: D) 120

Explanation:

K x 3/8 = 141 => K = 376

376 x 32.08/100 = 120

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