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:

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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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 8790
Q:

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

I. Two successive discount of 20% and 25%

II. Buy 5 get 3 free

III. Buy 5 get 6

 

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

Explanation:
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Q:

If 60% of a number is added to 60, then the result is equal to the number itself. What is the number?

 

A) 150   B) 120  
C) 100   D) 180  
 
Answer & Explanation Answer: A) 150  

Explanation:
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4 8750
Q:

The value of a machine depreciates at the rate of 10% every year. It was purchased 3 years ago. If its present value is Rs. 8,748, its purchase price was ?

A) Rs.14,000 B) Rs.12,000
C) Rs. 12,800 D) Rs. 15,000
 
Answer & Explanation Answer: B) Rs.12,000

Explanation:

We have P = 8748, R = -10 and n = 3
Therefore, the purchase price of the machine
= P1+R100n= 87481-101003
= 8748 x (100/90) x (100/90) x (100/90)
= 12,000.

 

Therefore, the purchase price of the machine was Rs. 12,000.

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7 8556
Q:

A Shepherd had n goats in the year 2000. In 2001 the no.of goats increased by 40% . In 2002 the no. of goats declined to 70%. In 2003 the no. of  goats grew by 30%. In 2004, he sold 10% goats, then he had only 34,398 goats. The percentage increase of the no.of goats in this duration was:

A) 14.66% B) 16.66%
C) 20% D) 33.33%
 
Answer & Explanation Answer: A) 14.66%

Explanation:

There is no need to use the no of goats i.e (34,398). let initially thete be 1000 goats then 

 

  1000 -----> 1400 -----> 980 -----> 1274 ----->1146.6

 

Thus the % increase = (1146.6-1000)/100 x 100= 14.66%

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7 8548
Q:

If 35% of a number is 24 less than 50% of that number, then the number is ?

A) 80 B) 160
C) 100 D) 120
 
Answer & Explanation Answer: B) 160

Explanation:

Let the number be n. Then,

50% of n - 35% of n = 24

50/100 n - 35/100 n = 24

n = (24 x 100)/15 = 160.

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Q:

In an election, there were two candidates only. The candidate who got 62% of the total votes polled and was elected by a majority of 192 votes. The total number of votes polled was?

Answer

Suppose total votes polled is x


\inline \Rightarrow \inline \frac{62x}{100}=\frac{38x}{100}+192


\inline \Rightarrow \frac{62x}{100}-\frac{38x}{100}=192


\inline \Rightarrow \frac{24x}{100}=192\Rightarrow x=800

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