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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6 9732
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 8965
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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8 8946
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 8884
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 8871
Q:

If 1/8 of a pencil is black, 1/2 of the remaining is white and the remaining, 3/2cm is blue. Find the total length of the pencil?

A) 8 cms B) 7 cms
C) 9 cms D) 11 cms
 
Answer & Explanation Answer: A) 8 cms

Explanation:

Let the total length of the pencil = x cms

From the given data,

'x/8' is black

Remaining part = x - x/8 = 7x/8

1/2 of 7x/8 is white

=> 7x/16 is white (Remaining part is 7x/16)

And given that the remaining part is blue and is 3 1/2 cm = 7/2 = 3.5 cm

That remaining part = 7x/16

Therefore,

7x/16 = 7/2

x = 16/2 = 8

Hence, the total length of the pencil = x = 8 cm.

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16 8871
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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Subject: Percentage

57 8709
Q:

Each edge of a cube is increased by 20% then the percentage increase in surface area of the cube is : 

A) 144% B) 40%
C) 44% D) 72.8%
 
Answer & Explanation Answer: C) 44%

Explanation:

The surface area of a cube = 6a2 =  6 side2

 

New  Surface area = 6 x 1.44a2

 

Therefore, 0.44a2a2x100 = 44%

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13 8549