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:

If the price of a commodity is decreased by 20% and its consumption is increased by 10%, what will be the increase or decrease in the expenditure on the commodity?

A) increase 12% B) decrease 12%
C) increase 16% D) decrease 16%
 
Answer & Explanation Answer: B) decrease 12%

Explanation:

Given the price of a commodity is decreased by  p = 20%

And its consumption is increased by q = 10%

Now, required increase or decrease in the expenditure on the commodity can be 

p + q + pq/100 = -20 + 10 - 200/100 = -10 - 2 = -12%.

 

Hence, decrease in the expenditure = 12%

 

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8 10398
Q:

A house owner wants to get his house painted. He is told that this would require 45 kg of paint allowing 6% wasting. And if the paint is available in 4 kg tins only, the number of tins required for painting the house is ?

A) 12 B) 13
C) 11 D) 10
 
Answer & Explanation Answer: A) 12

Explanation:

Given 45 kg for painting 

And 6% 0f 45 for wasting => 6x45/100 = 2.7 kg

Now total paint required = 45+2.7 = 47.7 kgs

But tins are available in only 4kgs

Then, no. of tins req = 47.7/4 = 11.4 => 12 tins

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14 10327
Q:

A shopkeeper offers the following 3 schemes. Which scheme has the maximum discount percentage?

 

I. Two successive discounts of 30% and 20%

 

II. Buy 4 get 7

 

III. Buy 4 get 3 free

 

A) Only I B) Only III  
C) Only II and III   D) All are equal
 
Answer & Explanation Answer: A) Only I

Explanation:
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1 10260
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

 

Students who like only Maths forms what percentage of the total number of students in the class?

 

A) 26.67% B) 24.22%
C) 28.80% D) 32.82%
 
Answer & Explanation Answer: A) 26.67%

Explanation:
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0 10256
Q:

In measuring the sides of a rectangle, one side is taken 20% in excess and the other 10% in deficit. Find the error per cent in area calculated from the measurement ?

A) 8% excess B) 9% deficit
C) 12% excess D) 11% deficit
 
Answer & Explanation Answer: A) 8% excess

Explanation:

Since  Area of Rectangle = side1 x side2
Therefore, error% in area
= x + y + xy100 %
= [20 - 10 + ( -10 x 20)/100]% or 8%
i.e. 8% excess.

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7 10198
Q:

If x is 90% of Y, what percent of x is y?

Answer

x = 90% of y = \inline \frac{9}{10}y


 


\inline \therefore \frac{x}{y}=\frac{9}{10}\Rightarrow \frac{y}{x}=\frac{10}{9} 


=> y = 1.1% of x.

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25 10116
Q:

Ramesh started a software business by investing Rs. 50,000. After six months, Rajesh joined him with a capital of Rs. 75,000. After 3 years, they earned a profit of Rs. 27,000. What was Rajesh's share in the profit?

A) 10,000 B) 15,000
C) 20,000 D) 25,000
 
Answer & Explanation Answer: B) 15,000

Explanation:


Ramesh : Rajesh =(50,000*36) : (75,000*30) =4 : 5.

Therefore, Rajesh's share=Rs.(27,000*5/9)= Rs.15,000.

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6 9932
Q:

5% of a number is 25% more than another number. The difference between the numbers is 96. Then find the value of the numbers?

A) 102 & 6 B) 99 & 3
C) 104 & 8 D) 100 & 4
 
Answer & Explanation Answer: D) 100 & 4

Explanation:

Let the first number be x and the second number be y.

Given

5% of x = (25% of y) + y

=> 5x/100 = 5y/4

=> x = 25y ......(1)

and also given that, x - y = 96

=> x = 96 + y .....(2)

From (1)&(2)

25y = 96 + y

=> 24y = 96

=> y = 4

From (1)

x = 96 + 4 = 100

Hence, the numbers are 100 & 4.

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15 9375