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:

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 10558
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 10363
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 10184
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 9950
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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17 9634
Q:

Solve 30 + (.0825 x 30) + (15% x 30)

A) 24.750 B) 36.975
C) 34.652 D) 26.354
 
Answer & Explanation Answer: B) 36.975

Explanation:

30 + (.0825 x 30) + (15% x 30)

 

Now

=> 0.0825 x 30 = 2.475 -----(1)

=> 15% of 30 = 450/100 = 4.5 -----(2) 

 

Hence, from (1) & (2)

30 + (.0825 x 30) + (15% x 30)

= 30 + 2.475 + 4.5

30 + (.0825 x 30) + (15% x 30) = 36.975.

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19 9581
Q:

In an election only two candidates contested. A candidate secured 70% of the valid votes and won by a majority of 172 votes. Find the total number of valid votes  ?

A) 446 B) 415
C) 404 D) 430
 
Answer & Explanation Answer: D) 430

Explanation:

Let the total number of valid votes be 'V'.

70% of V = 70/100 x V = 7V/10

Number of votes secured by the other candidate = V - 7V/100 = 3V/10

Given, 7V/10 - 3V/10 = 172 => 4V/10 = 172

=> 4V = 1720 => V = 430.

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8 9461
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 9270