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:

A woman suffered 20% loss on first investment and made 10% profit at second investment and 12 ½% profit on the third investment. If the invested amount be in the ratio of 4 : 5 : 3, find her profit percentage?

A) 0.625% B) 1.205%
C) 0.987% D) 0%
 
Answer & Explanation Answer: A) 0.625%

Explanation:

From the given data,

let the amounts invested be 4p, 5p and 3p

Net profit = Total profit - Total loss

= 10x5p/100 + 25x3p/200 - 20x4p/100

= 0.875p - 0.8p

= 0.075p

Therefore, profit% = (Net profit/Total investment) x 100

= 0.075 x 100/12 

= 0.0625%

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9 2791
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:

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

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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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6 2629
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

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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 percentage of students who passed in all subjects?

A) 8 B) 12
C) 7 D) 10
 
Answer & Explanation Answer: C) 7

Explanation:
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