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:

The percentage of metals in a mine of zinc ore is 60%. Now the percentage of silver is 3/4% of metals and the rest is zinc. If the mass of ore extracted from the mine is 8000 kg, the mass (in kg) of zinc is

A) 5147 kg B) 4764 kg
C) 3587 kg D) 2125 kg
 
Answer & Explanation Answer: B) 4764 kg

Explanation:

Mass of zinc ore = 8000 kg


Mass of metal = 60% of 8000 = 4800 kg


Mass of silver in metal = 3/4 x 4800/100 = 36 kg


Mass of zinc = 4800 - 36 = 4764 kg.

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Q:

A man wills 25% of his wealth to charity and rest to his family. What percent of the wealth willed to charity does the family get?

A) 200 B) 33.3
C) 300 D) 25
 
Answer & Explanation Answer: C) 300

Explanation:
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Q:

125% as a Fraction?

A) 1/4 B) 3/4
C) 5/4 D) 7/4
 
Answer & Explanation Answer: C) 5/4

Explanation:

Literally any percentage means divide by 100.

So 125% = 125100. That can be reduced to 5/4.

To convert to a decimal, you can do long division, dividing 5 into 4.

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Q:

36 of what number is 18?

A) 38 B) 42
C) 50 D) 62
 
Answer & Explanation Answer: C) 50

Explanation:

Let the required number be 'p'

36 of what number is 18 implies 36% of p = 18

=> 36 x p/100 = 18

=> p = 1800/36

=> p = 50.

 

Hence, 36% of 50 is 18.

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Q:

Dot cabs company provides cabs for software employees. The company has 8 Swift dzires, 6 Scorpios, 7 Innovas and few small cars. If Swift dzire makes one fourth of the total fleet, how many small cars are there in the company ?

A) 9 B) 10
C) 11 D) 12
 
Answer & Explanation Answer: C) 11

Explanation:

Given the company has 8 SD + 6 SRP + 7 IN = 21 cars + 'x' small cars.
Given SD makes 1/4 th of the total fleet.
=> 8 = 1/4 (21 + x)
=> 32 = 21 + x
=> x = 11
Therefore, the company has 11 small cars.

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Q:

Write 0.125 as a percent %?

A) 12% B) 12.5%
C) 13% D) 13.5%
 
Answer & Explanation Answer: B) 12.5%

Explanation:

Here to convert 0.125 into %

First convert to fractio

Multiply and divide by 1000

=> 0.125 x 10001000 = 1251000 = 18

=> Now, in percentage18 x 100 = 12.5%

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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) 1020 D) 920
 
Answer & Explanation Answer: A) 1060

Explanation:

Total number of sweets

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

= 960 + 100 = 1060

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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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