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 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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Q:

The length of a rectangular plot is increased by 50%, to keep its area unchanged, the width of the plot should be decreased by ______?

A) 29.87% B) 33.33%
C) 22.22% D) 19.5%
 
Answer & Explanation Answer: B) 33.33%

Explanation:

% Decrease in Width = 50150x100

 

= 33.33% 

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13 5389
Q:

In a class 60% of the students pass in English and 45% pass in Hindi. If 25% of them pass in both subjects, what percentage of the students fail in both the subjects?

A) 20% B) 25%
C) 30% D) 15%
 
Answer & Explanation Answer: A) 20%

Explanation:

Percentage of students passed in English = 60%

Percentage of students passed in Hindi = 45%

Percentage of students passed in both subjects = 25%

ATQ,

Percentage of students passed in only English = 60 - 25 = 35%

Percentage of students passed in only Hindi = 45 - 25 = 20%

Therefore, Percentage of students failed = 100 - (35 + 25 + 20)

= 100 - 80 = 20%.

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6 5354
Q:

The price of an item is decreased by 25%. What percent increase must be done in new price to get the original price?

A) 33.33% B) 43.3%
C) 50% D) 55.3%
 
Answer & Explanation Answer: A) 33.33%

Explanation:

Let the price of an item be 100After 25% decrease, price of item = 75Increase in price to get the original price = 100-75 = 25% increase to get the original price = 25/75 X 100 = 100/3 = 33.33%

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Q:

There are 600 Kabaddi players 4% wear knee band on one leg. Of the remaining, 25% wear knee bands on both legs. How many players don't wear a knee band ?

A) 426 B) 428
C) 415 D) 432
 
Answer & Explanation Answer: D) 432

Explanation:

There are 600 Kabaddi players
4% wear knee band on one leg
Remaining players = 600 x 0.96 = 576
Of the remaining, 25% wear knee bands on both leg
and Of the remaining, 75% do not wear knee bands .
So players not wearing knee bands = 0.75 x 576 = 576 x 3/4 = 144 x 3 = 432.

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5 5276
Q:

15% of 60 is 45% of __

 

A) 20 B) 30
C) 180 D) 40
 
Answer & Explanation Answer: A) 20

Explanation:
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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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Q:

A girl want to read a complete book. She read 2/5 part of a book on 1st day, 34% on second day and remaining pages in next two days. On those two days she read equal number of pages. If she read 52 pages on last day, then find out total number of pages that the book contain ?

A) 400 B) 525
C) 325 D) 475
 
Answer & Explanation Answer: A) 400

Explanation:

Let the total number of pages in the book be 'x'.

From given data,

2x/5 + 34x/100 + 52 + 52 = x

 => 40x + 34x + 10400 = 100x

 => 26x = 10400

 => x = 400.

 Hence, total pages in the book are 400.

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