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:

Two numbers are 35% and 42% are less than a third number .How much percent is the second number less than the first ?

A) 10.769 % B) 11.23 %
C) 10.4 % D) 9.87 %
 
Answer & Explanation Answer: A) 10.769 %

Explanation:

I      II     III

65   58   100

65 -------- 7
100 ------ ?  => 10.769%

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12 15571
Q:

The salary of Mr. X is 30% more than that of Mr. Y . Find what percent of Mr. Y’s salary is less than Mr. X’s ?

A) 24% B) 23 1/3%
C) 25 1/2% D) 22 8/9 %
 
Answer & Explanation Answer: B) 23 1/3%

Explanation:

y=100 x=130

130---------30
100---------? => 23 1/3%

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Q:

A number X is mistakenly divided by 10 instead of being multiplied by 10. What is the percentage error in the result?

A) -99% B) +99%
C) -100% D) +100%
 
Answer & Explanation Answer: A) -99%

Explanation:

By mistake = x/10 

 

Actual value = x * 10 

 

% Change = 10x-x1010x×100 = 99100×100  = 99% (negative)

 

Since actual value is greater than the wrong value.

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15 15234
Q:

A man lost half of its initial amount in the gambling after playing 3 rounds. The rule of gambling is that if he wins he will receive Rs. 100, but he has to give 50% of the total amount after each round.Luckily he won all the three rounds. The initial amount with which he had started the gambling was :

A) 500/3 B) 700/3
C) 300 D) 600
 
Answer & Explanation Answer: B) 700/3

Explanation:

Let the initial amount be x (with gambler), then 

 x+10012 + 10012+10012 = x2

=> x = 700/3

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20 15178
Q:

A batsman scored 120 runs which included 3 boundaries and 8 sixes. What percent of his total score did he make by running between the wickets ?

A) 40% B) 45%
C) 50% D) 55%
 
Answer & Explanation Answer: C) 50%

Explanation:

Number of runs made by running = 120 - (3 x 4 + 8 x 6) = 120 - (60) = 60 

Required percentage = [(60/120)*100] % = 50%

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30 15082
Q:

The price of a cycle is reduced by 25 per cent. The new price is reduced by a further 20 per cent. The two reductions together are equal to a single reduction of

A) 45% B) 40%
C) 35% D) 32.5%
 
Answer & Explanation Answer: B) 40%

Explanation:

Let the original price of the cycle be 100. After the first reduction the price will be 75.

This new price is then reduced by 20% = 0.8 x 75 = 60

60 represents a reduction of 40 percent on the original.

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Q:

A shopkeeper offers the following 3 schemes. Which scheme has the maximum discount percentage?

I. Two successive discount of 20% and 25%

II. Buy 5 get 3 free

III. Buy 5 get 6

 

A) Only II B) Only I
C) Only I and II D) Only I and III
 
Answer & Explanation Answer: B) Only I

Explanation:
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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

Explanation:
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