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:

In a school of 1500 boys, 35% are Hindu, 30% are Sikh,15% are Muslims and remainning are Christians. Find number of christian boys in the school ?

Answer

Given total number of boys in the school = 1500


In that 35% are Hindu, 30% are Sikh, 15% are Muslims


=> 35 + 30 + 15 = 80%


Remaining Boys = 100% - 80% = 20% of 1500


=> 20 x 1500/100 = 300 boys are Christians. 

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5 6269
Q:

P, Q and R secured 45%, 50% and 60% marks respectively in Biology. M’s marks in Biology is 12.5 more than P’s marks and 4 less than R’s marks. Find out the individual marks of four students.

 

A. For the students, total marks obtained for Biology is 311.5.
B. Total of M’s and P’s marks in Biology is 147.5.
C. R has obtained 84 marks.

A) Only C B) Only A & B
C) All are required D) None of the statements is required
 
Answer & Explanation Answer: D) None of the statements is required

Explanation:

From the given data,
(60 - 45)% = 12.5 + 4
15% = 16.5
=> 100% = ?
100% = 16.5 x 100/15 = 110

Hence, P = 45% of 110 = 45x110/100 = 49.5
Q = 50% of 110 = 55
R = 60% of 110 = 60 x 110/100 = 66
M = 12.5 + 49.5 = 62 or 66 - 4 = 62

 

Hence, no statement is required to answer.

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3 6258
Q:

Which value is equal to 5% of 1,500?

A) 35 B) 55
C) 75 D) 45
 
Answer & Explanation Answer: C) 75

Explanation:

In the question it is asked for 5% of 1500

5 x 1500/100 = 15 x 5 = 75.

 

Hence, 5% of 1,500 is equal to 75.

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10 6238
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 6146
Q:

If three eighth of a number is 141. What will be the approximately value of 32.08% of this number ?

A) 101 B) 112
C) 104 D) 120
 
Answer & Explanation Answer: D) 120

Explanation:

K x 3/8 = 141 => K = 376

376 x 32.08/100 = 120

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5 6138
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 6091
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 6045
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 6036