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:

An engineering student has to secure 24% marks to pass. He gets 61 and fails by 29 marks. What is the maximum marks for that exam?

A) 375 marks B) 400 marks
C) 425 marks D) 450 marks
 
Answer & Explanation Answer: A) 375 marks

Explanation:
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Q:

Twenty percent of Karthik’s monthly salary is equal to thirty two percent of Nikitha’s monthly salary. Vipin’s monthly salary is four fifth that of Nikitha’s monthly salary. If Vipin’s annual salary is Rs. 3.84 lakhs, what is Karthik’s monthly salary?

A) 32,000 B) 64,000
C) 40,000 D) 52,000
 
Answer & Explanation Answer: B) 64,000

Explanation:

From the given data,

20% of K = 32% of N

V = 4/5 N

 

Given Vipin's salary = 3.84 lpa = 3.84/12 = 32,000 per month

Now, N = 5/4 x 32000 = 40000

Now K = 32/20 x 40000 = 64000

 

Hence, karthik's monthly salary = Rs. 64000.

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Q:

In a hostel the rent per room is increased by 20%. If number of rooms in the hostel is also increased by 20% and the hostel is always full, then what is the percentage change in the total collection at the cash counter?

A) 30% B) 40%
C) 44% D) 48%
 
Answer & Explanation Answer: C) 44%

Explanation:
Let initial rent be rs 10
And initial rooms be 10
So initial collection = 10*10 = Rs 100
Now new rent = 10 + 20% of 10 = 12
New no of rooms = 10 + 20% of 10 = 12
So new collection = 12*12 = 144
% change in collection = (144-100)/100*100 = 44%
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Q:

In a test, 14% of the students failed in Maths and 22% failed in Hindi. If 18% of the students failed in both the subjects, then the percentage of students who passed in both the subjects is

A) 46 B) 44
C) 42 D) 40
 
Answer & Explanation Answer: A) 46

Explanation:

Let the number of students = 100

Number of students who failed in one or more subjects = 14 + 22 + 18 = 54%

The percentage of students who passed in both the subjects = 100 - 54 = 46%.

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Q:

The costs of daily ticket of local train is Rs 160 and Monthly Pass costs Rs 2912. If I buy the Monthly Pass and travel for 26 days in a month then I save?

A) 25 percent B) 22 percent
C) 18 percent D) 30 percent
 
Answer & Explanation Answer: D) 30 percent

Explanation:
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Q:

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

 

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

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Q:

Due to increase of 33.33% in the price of apples, a customer can purchase 4 apples less for Rs 16. What is the original price (in paise) of an apple?

A) 100 B) 125
C) 150 D) 400/3
 
Answer & Explanation Answer: A) 100

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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

 

How many students like exactly one subject?

A) 16 B) 12
C) 6 D) 22
 
Answer & Explanation Answer: D) 22

Explanation:
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