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:

If 60% of a number is added to 60, then the result is equal to the number itself. What is the number?

 

A) 150   B) 120  
C) 100   D) 180  
 
Answer & Explanation Answer: A) 150  

Explanation:
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Q:

In an election only two candidates contested 20% of the voters did not vote and 120 votes were declared as invalid. The winner got 200 votes more than his opponent  thus he secured 41% votes of the total voters on the voter list. Percentage votes of the defeated candidate out of the total votes casted is:

A) 47.5% B) 41%
C) 38% D) 45%
 
Answer & Explanation Answer: D) 45%

Explanation:

Let there be x voters and k votes goes to loser then 

 

      0.8x - 120 = k + (k + 200)

 

         k+200 = 0.41x

 

 => k = 1440

 

and  (k + 200) =1640

 

Therefore  1440/3200 x 100 = 45%

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Q:

What is the value of 88% of 1125 + 20% of 425?

 

A) 1025 B) 1125.2
C) 1075 D) 1055
 
Answer & Explanation Answer: C) 1075

Explanation:
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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:

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:

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:

What percent of 7.2 kg is 18 gms ?

A) .25% B) .5%
C) .75% D) 1%
 
Answer & Explanation Answer: A) .25%

Explanation:

Required percentage = (18/7200 * 100)% =  1/4% = 0.25%

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Q:

A number is decreased by 10% and then increased by 10%.  The number so obtained is 10 less than the original number. What was the oiginal number ? 

A) 1000 B) 2000
C) 3000 D) 4000
 
Answer & Explanation Answer: A) 1000

Explanation:

Let the original number be x.

 

Final number obtained = 110% of (90% of x) =(110/100 * 90/100 * x) = (99/100)x. 

 

x-(99/100)x=10

=> x =1000

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