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:

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 6833
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 6643
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 6543
Q:

If there are 150 questions in a 3 hr examination. Among these questions 50 are type A problems, which requires twice as much as time be spent on the rest of the type B problems. How many minutes should be spent on type A problems ?

A) 75 min B) 82 min
C) 90 min D) 101 min
 
Answer & Explanation Answer: C) 90 min

Explanation:

Let X = Time taken for each of Type B Problems(100 Problems)
And 2X = Time taken for each of Type A problems(50 problems)

Total time period = 3hrs = 3 x 60min = 180 minutes

100X + 50(2X) = 180
100X + 100X = 180
200X = 180 min

X = 180/200
X = 0.90 min

By convertiing into seconds,

X = 0.90 x 60 seconds
X = 54 sec

So, time taken for Part A problems is = 54 x 2 x 50 = 5400 seconds
= 5400/60sec = 90 minutes.

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8 6541
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 6514
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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7 6466
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 6363
Q:

A shopkeeper’s earning increases by 25% in first year but decreases by 4% in the next and so on. After 5 years his total earnings would be Rs. 72,000. What is his present earning?

A) Rs. 40,000 B) Rs. 45,000
C) Rs. 42,000 D) Rs. 46,000
 
Answer & Explanation Answer: A) Rs. 40,000

Explanation:

Let his present earnings be Rs. p

ATQ,

(125/100) x (96/100) x (125/100) x (96/100) x (125/100) x p = 72000

p = Rs. 40,000.

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27 6283