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:

An individual deposited 20% of 25% of 30% of what he had into his account with a bank. If he deposited Rs.750, how much was he having initially with him before depositing ?

A) Rs. 38000 B) Rs. 47000
C) Rs. 50000 D) Rs. 35000
 
Answer & Explanation Answer: C) Rs. 50000

Explanation:

Let 'x' be the amount he had in the bank.

=> 20/100(25/100(30/100(x))) = 750

x = 750 x 8000/120 = Rs. 50000

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Q:

Ajay who is a King, at his eleventh hour, called his three queens and distributed his gold in the following way: He gave 50% of his wealth to his first wife, 50% of the rest to his second wife and again 50% of the rest to his third wife. If their combined share is worth1,30,900 kilograms of gold, find the quantity of gold King Ajay was having initially?

A) 153145 kgs B) 147890 kgs
C) 152400 kgs D) 149600 kgs
 
Answer & Explanation Answer: D) 149600 kgs

Explanation:

Let the total quantity of gold be p kgs.

According to the question,

50% of p + 25% of p + 12.5% of p = 130900

87.5% of p = 130900

p = 130900 x 100/87.5  = 149600 kgs.

 

Therefore, the initial gold quantity that king has = p = 149600 kgs.

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Q:

In one year, the Amount collected for social welfare, of a village increased by 10% and in the next year, it decreased by 10%. If at the end of 2nd year, the amount was 7920, what was it in the beginning ?

A) 8800 B) 8650
C) 8000 D) 8980
 
Answer & Explanation Answer: C) 8000

Explanation:

Let the amount collected be 'A'
Then, from the given conditions,
A x 110/100 x 90/100 = 7920
A x 0.99 = 7920
A = 7920/0.99
=> 8000

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Q:

Arun’s weight is 140% of Akhil’s weight. Nani’s weight is 90% of Shreyon’s weight. Shreyon’s weight is twice as much as Akhil’s. What percentage of Arun’s weight is Nani’s weight?

A) 76% B) 77%
C) 78% D) 79%
 
Answer & Explanation Answer: C) 78%

Explanation:

Let Akhil's weight = p kg

=> Shreyon's weight = 2p kg

Nani's weight = 0.9 x 2p = 1.8p kg

=> Arun's weight = 1.4p kg

Required percentage = 1.4p1.8p x 100

= 77.8%

~= 78%

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Q:

The marked price of a Watch is Rs.8400. It is to be sold at Rs.6896 at two successive discounts. If the first discount is 12%, the second discount is ?

A) 7.2 % B) 9.14 %
C) 7.13 % D) 6.709 %
 
Answer & Explanation Answer: D) 6.709 %

Explanation:

(100-x)%  of 88% of 8400 = 6896

 

=> 100-x10088100x8400 = 6896


=> x = 6.709%

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Q:

A restaurant offers a new promotion of 20% off the original price of cakes, which is Rs. 12. Before the promotion 250 cakes were sold each day. After the promotion, the sale of cakes increases an average of 18% more per day. How much more or less does the restaurant make each day in cakes sales after the promotion?

A) Rs. 185 less B) Rs. 202 more
C) Rs. 175 more D) Rs. 168 less
 
Answer & Explanation Answer: D) Rs. 168 less

Explanation:

Cost of each cake P1 & P2 = Rs. 12

Offer decrease in % = 20%

Increase in sale per day (Q2) = 250 - 18%

Total quantity per day (Q1) = 250

Hence, required change total revenue

TR = P2Q2 - P1Q1 = (12 x 0.8 x 250 x 1.18) -  (12 x 250) = - Rs.168.

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Q:

Kalyan purchased a Maruti van for Rs. 1,96,000 and the rate of depreciation is 14(2/7) % per annum. Find the value of the van after two years ?

A) Rs. 1,24,000 B) Rs. 1,44,000
C) Rs. 1,32,000 D) Rs. 1,62,000
 
Answer & Explanation Answer: B) Rs. 1,44,000

Explanation:

Value of Maruti Van, V1 = Rs. 1,96,000
Rate of depreciation, r = 14(2/7)% = 100/7%; Time, t = 2 years
Let V2 is the value after depreciation.

V2 = V11 - r100t
V2 = 196001 - 10071002

V2 = 196000(6/7)(6/7)

V2 = (196000x36)/49 = Rs. 1,44,000.

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Q:

3 is what percent of 5?

A) 45% B) 60%
C) 72% D) 80%
 
Answer & Explanation Answer: B) 60%

Explanation:

Here it is asked that 3 is what percent of 5

Let 3 is K percent of 5.

=> K x 5/100 = 3

=> K = 300/5 = 60

 

Hence, 3 is 60% of 5.

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