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:

12 as a percentage?

A) 50% B) 5%
C) 0.5% D) 0.05%
 
Answer & Explanation Answer: A) 50%

Explanation:

1/2 as a percentage means

1/2 = 0.5 in decimal

Now, in percentage means 0.5 x 100% = 50%.

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8 5961
Q:

A duster is of dimension 5x5x7 all in cms,  is sinked into a cylindrical vessel of radius 5 cm and height 10 cm. After insertion the level of the water is inccresed by 2.14 cm. Then by what percentage the part of the duster is above the layer ?

A) 96 % B) 4 %
C) 97 % D) 3 %
 
Answer & Explanation Answer: B) 4 %

Explanation:

Imension of the duster is assumed as 5x5x7 cm3

Volume of the duster below the water layer
= volume of water increased
= πxrxrxh = 3.14×52×2.14 ≈ 168 cm3

Total volume of the duster = 5×5×7 = 175 cm3

Percentage of the duster part below the layer = 168×100/175 = 96%

Percentage of the duster part above the layer = 4%

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4 5959
Q:

A merchant commences with a certain capital and gains annually at the rate of 30 per cent. At the end of 2 years he has worth Rs 10,000. What was the original capital? 

A) Rs. 4987 B) Rs. 5148
C) Rs. 5917 D) Rs. 6254
 
Answer & Explanation Answer: C) Rs. 5917

Explanation:

Let the Original capital amount be Rs. P

Given after 2 years the amount is Rs. 10000

Rate of interest = 30%

According to the question,

P x 130100 x 130100 = 10000=> P = 1000000169 = 5917

Therefore, the capital amount P = Rs. 5917

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6 5916
Q:

Read the data given and answer the following questions

 

In a class of 60 students:

 

42 like Maths,

32 like English,

12 like neither Maths nor English

 

How many students like exactly one subject?

A) 16 B) 12
C) 6 D) 22
 
Answer & Explanation Answer: D) 22

Explanation:
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0 5905
Q:

A sales boy is allowed 412 % discount on the total sales made by him plus a bonus of 14% on the sales over Rs.12,000.If his total earnings were Rs.2400, then his total sales(in Rs.) are ?

A) Rs.60,145.23 B) Rs.54,285.54
C) Rs.52,147.85 D) Rs.50,589.47
 
Answer & Explanation Answer: D) Rs.50,589.47

Explanation:

Let the total earnings be Rs.x 

Then 412% of x + 14% of (x-12000) =2400

 92×x100+14×x-12000100=2400

=>  x=50,589.47

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8 5896
Q:

Read the data given below and answer the questions based on it.

 

In the CBSE Board exams last year, 53% passed in Biology, 61% percent passed in English, 60% in Social studies, 24% in Biology and English, 35% in English and social studies, 27% in Biology and social studies and 5% in none.

 

If the number of students in the class is 200, how many passed in only one subject?

A) 48 B) 46
C) More than 50 D) Less than 40
 
Answer & Explanation Answer: B) 46

Explanation:
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3 5855
Q:

The length of a rectangular plot is increased by 50%, to keep its area unchanged, the width of the plot should be decreased by ______?

A) 29.87% B) 33.33%
C) 22.22% D) 19.5%
 
Answer & Explanation Answer: B) 33.33%

Explanation:

% Decrease in Width = 50150x100

 

= 33.33% 

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13 5783
Q:

80% of 900 + 162 x 4 x ? = 113 - 99

A) 0.5 B) 1
C) 4 D) 0
 
Answer & Explanation Answer: A) 0.5

Explanation:

80x900/100 + 256 x 4 x ? = 1331 - 99

720 + 1024 x ? = 1232

? = 1232 - 720/1024

? = 512/1024 = 0.5

? = 0.5 

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11 5754