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:

15% of 60 is 45% of __

 

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

Explanation:
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4 23767
Q:

In some quantity of ghee, 60% is pure ghee and 40% is vanaspati. If 10 kg of pure ghee is added, then the strength of vanaspati ghee becomes 20%. The original quantity was : 

A) 10 kg B) 15 kg
C) 20 kg D) 25 kg
 
Answer & Explanation Answer: A) 10 kg

Explanation:

Let the original quantity be x kg. Vanaspati ghee in x kg  =  (40x / 100 )kg = (2x / 5) kg. 

Now, (2x/5)/(x + 10) = 20/100

=> 2x / (5x + 50) = 1/5 

=> 5x = 50 

=> x = 10.

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54 23692
Q:

In an examination, 34% of the students failed in Mathematics and 42% faiied in English. If 20% of the students failed in both the subjects, then the percentage of students who passed in both the subjects was :

A) 34 % B) 44 %
C) 54 % D) 64 %
 
Answer & Explanation Answer: B) 44 %

Explanation:

n (A) = 34, n (B) = 42, n (A   B) = 20.

 

So, n (A  U B) = n (A) + n(B) - n(A B) = 34 + 42 - 20 = 56.

 

Percentage failed in either or both the subjects = 56.

 

Hence, percentage passed = (100 - 66)% = 44%.

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28 23436
Q:

How many litres of pure acid are there in 8 litres of a 20% solution ?

A) 1.4 B) 1.5
C) 1.6 D) 1.7
 
Answer & Explanation Answer: C) 1.6

Explanation:

Quantity of pure acid = 20% of 8 litres = ((20/100)*8) litres = 1.6 litres.

 

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Q:

Read the data given below and answer the questions based on it.

 

In the CBSE Board exams last year, 53% passed in Biology, 61% percent passed in English, 60% in Social studies, 24% in Biology and English, 35% in English and social studies, 27% in Biology and social studies and 5% in none.

 

If the number of students in the class is 200, how many passed in only one subject?

A) 48 B) 46
C) More than 50 D) Less than 40
 
Answer & Explanation Answer: B) 46

Explanation:
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Q:

Read the data given and answer the following questions

 

In a class of 60 students:

 

42 like Maths,

32 like English,

12 like neither Maths nor English

 

Students who like only Maths forms what percentage of the total number of students in the class?

 

A) 26.67% B) 24.22%
C) 28.80% D) 32.82%
 
Answer & Explanation Answer: A) 26.67%

Explanation:
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Q:

What percent of a day is 3 hours?

A) 14.9% B) 12.5%
C) 15.6%% D) 11.4%
 
Answer & Explanation Answer: B) 12.5%

Explanation:

Let p% of a day is 3 hrs.

We know that a day has 24 hrs.

=> p x 24/100 = 3

=> p = 300/24

=> p = 12.5%

 

Hence, 3 hrs is 12.5% of a day.

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24 22346
Q:

In a competitive examination in State A, 6% candidates got selected from the total appeared candidates. State B had an equal number of candidates appeared and 7% candidates got selected with 80 more candidates got selected than A. What was the number of candidates appeared from each State ?

A) 4000 B) 8000
C) 12000 D) 16000
 
Answer & Explanation Answer: B) 8000

Explanation:

Let the number of candidates appeared from each state be x.

In state A, 6% candidates got selected from the total appeared candidates

In state B, 7% candidates got selected from the total appeared candidates

But in State B, 80 more candidates got selected than State A

From these, it is clear that 1% of the total appeared candidates in State B = 80

=> total appeared candidates in State B = 80 x 100 = 8000

=> total appeared candidates in State A = total appeared candidates in State B = 8000

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