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:

While purchasing one item costing Rs. 400, I had to pay the sales tax at 7% and on another costing Rs. 6400, the sales tax was 9%. What percent of the sales tax I had to pay, taking the two items together on an average ?

A) 8 + 15/17 B) 2 + 13/17
C) 3 + 2/17 D) 5 + 13/12
 
Answer & Explanation Answer: A) 8 + 15/17

Explanation:

Total sales tax paid = 7% of Rs, 400 + 9% of Rs. 6400

                            =Rs. (7/100)*400 + (9/100)*6400 = Rs. (28 + 576) = Rs. 604. 

 

Total cost of the items = Rs. (400 + 6400) = Rs. 6800.

 

Required percentage =(604/6800*100) % = 81517%.

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Q:

In a test, minimum passing percentage for girls and boys is 35% and 40% respectively. A boy scored 483 marks and failed by 117 marks. What is the minimum passing marks for girls ?

A) 625 B) 525
C) 425 D) 325
 
Answer & Explanation Answer: B) 525

Explanation:

Given 40% minimum passing marks for boys = 483 + 117 = 600
=> 1% = 600/40
=> 100% = 600 x 100/40 = 1500
Minimum passing marks for girls = 35% of 1500 = 35 x 1500/100 = 525.

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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 14843
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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8 14343
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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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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19 14253
Q:

Fresh grapes contain 60% water, while dry grapes contain 40% water. How many kgs of dry grapes can be obtained by 60 kg of fresh grapes?

A) 25 kgs B) 30 kgs
C) 35 kgs D) 40 kgs
 
Answer & Explanation Answer: D) 40 kgs

Explanation:

The fruit content in both the fresh fruit and dry fruit is the same.

Let 'p' kgs of dry grapes are obtained from the 60 kgs of fresh grapes

 

=> 60 x 40100 = p x 60100=> p = 40 kgs.

 

Therefore, 40 kgs of Dry grapes are obtained from 60 kgs of Fresh grapes.

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Q:

What percent of a day is 3 hours?

A) 14.9% B) 12.5%
C) 15.6%% D) 11.4%
 
Answer & Explanation Answer: B) 12.5%

Explanation:

Let p% of a day is 3 hrs.

We know that a day has 24 hrs.

=> p x 24/100 = 3

=> p = 300/24

=> p = 12.5%

 

Hence, 3 hrs is 12.5% of a day.

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