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 merchant commences with a certain capital and gains annually at the rate of 30 per cent. At the end of 2 years he has worth Rs 10,000. What was the original capital? 

A) Rs. 4987 B) Rs. 5148
C) Rs. 5917 D) Rs. 6254
 
Answer & Explanation Answer: C) Rs. 5917

Explanation:

Let the Original capital amount be Rs. P

Given after 2 years the amount is Rs. 10000

Rate of interest = 30%

According to the question,

P x 130100 x 130100 = 10000=> P = 1000000169 = 5917

Therefore, the capital amount P = Rs. 5917

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6 6035
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 5933
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 5911
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 5885
Q:

In a class of 80 students and 5 teachers, each student got sweets that are 15% of the total number of students and each teacher got sweets that are 25% of the total number of students. How many sweets were there?

A) 1060 B) 960
C) 860 D) 760
 
Answer & Explanation Answer: A) 1060

Explanation:

From the given data,

80 x 15/100 of 80 + 5 x 80 x 25/100

= 960 + 100

= 1060.

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9 5853
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 5802
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 5799
Q:

Prasanna invested certain amount in three different schemes X, Y and Z with the rate of interest 10% p.a, 12% p.a and 15% p.a respectively. If the total interest accrued in one year was Rs. 3200 and the amount invested in Scheme Z was 150% of the amount invested in Scheme X and 240% of the amount invested in Scheme Y, what was the amount invested in Scheme Y by Prasanna ?

A) Rs.6000 B) Rs.4500
C) Rs.7500 D) Rs.5000
 
Answer & Explanation Answer: D) Rs.5000

Explanation:

Let a, b and c be the amounts invested in schemes X, Y and Z respectively. Then,

As we know:

Simple interest (S.I.) = PTR/100

(a × 10 × 1/100) + (b × 12 × 1/100) + (c × 15 × 1/100) = 3200

= 10a + 12b + 15c = 320000 .........(1)

Now, c = 240% of b = 12b/5 .........(2)

And, c = 150% of a = 3a/2 => a = 2/3 c = (2 × 12)b/(3 × 5) = 8b/5 .......(3)

From (1), (2) and (3), we have

16b + 12b + 36b = 320000 => 64b = 320000 => b = 5000

∴ Sum invested in Scheme Y = Rs.5000.

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9 5576