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:

30% of a number is 33. What is the number?

 

A) 120 B) 115
C) 105 D) 110
 
Answer & Explanation Answer: D) 110

Explanation:
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Q:

If A is 40% less than B, then B is how much percentage more than A?

 

 

A) 72.33 B) 60
C) 40 D) 66.66
 
Answer & Explanation Answer: D) 66.66

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Q:

The sum of the number of boys and girls in a school is 150. if the number of boys is x, then the number of girls becomes x% of the total number of students. The number of boys is : 

A) 60 B) 70
C) 80 D) 90
 
Answer & Explanation Answer: A) 60

Explanation:

We have : x + (x% of 150 )= 150 

=> x+(x/100)*150] = 150

=> 52x = 150  

=> x = (150*2)/5 = 60

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Q:

Selling price of an article is Rs 2397 and discount offered is 15%. What is the marked price (in Rs)?

 

A) 2756.5 B) 2856.6
C) 2740 D) 2820
 
Answer & Explanation Answer: D) 2820

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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.

 

What is the ratio of percentage of students who passed in Biology and Social Studies but not English in relation to the percentage of students who passed in Social Studies and English but not Biology?

A) 5:7 B) 7:5
C) 4:5 D) 5:4
 
Answer & Explanation Answer: A) 5:7

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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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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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Q:

The CO2 emissions in million metric tons over 3 years are given in the following table.

 

What is the increase in the percentage of CO2 emission from year 2016 to 2017?

A) 36.36% B) 26.36%
C) 63.63% D) 36.45%
 
Answer & Explanation Answer: A) 36.36%

Explanation:
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