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:

Solve 30 + (.0825 x 30) + (15% x 30)

A) 24.750 B) 36.975
C) 34.652 D) 26.354
 
Answer & Explanation Answer: B) 36.975

Explanation:

30 + (.0825 x 30) + (15% x 30)

 

Now

=> 0.0825 x 30 = 2.475 -----(1)

=> 15% of 30 = 450/100 = 4.5 -----(2) 

 

Hence, from (1) & (2)

30 + (.0825 x 30) + (15% x 30)

= 30 + 2.475 + 4.5

30 + (.0825 x 30) + (15% x 30) = 36.975.

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19 6731
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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7 6387
Q:

What is better, to have 70% discount or 40 and 30% discount consequently ?

A) 40% is better B) 70% is better
C) Both are same D) None
 
Answer & Explanation Answer: B) 70% is better

Explanation:

Let Price be Rs.100

1st CASE:

Then 100 x 70/100 = 70
=> price after discount = 100-70 = Rs.30

2nd CASE:

Then 100 x 40/100 = 40
=> price after discount = 100-40 = Rs.60
then
60 x 30/100 = 18
=> price after 2 consequent discount = 60-18 = Rs.42

=>from 1 and 2 cases, 70% discount is better.

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10 6353
Q:

30% of 500 rupees is?

A) Rs. 180 B) Rs. 150
C) Rs. 120 D) Rs. 240
 
Answer & Explanation Answer: B) Rs. 150

Explanation:

Given 30% of 500

= 30100 x 500= 30 x 5= 150

 

Hence, 30% of Rs. 500 = Rs. 150.

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19 6350
Q:

Subbu purchased a tape recorder at 9/10 of its selling price and sold it at 8% more than its selling price. His gain is

Answer

Let S.P = x then C.P = \inline \frac{9x}{10}


Selling price received by subbu = (108% of x)


                                            = \inline \frac{108}{100}x=\frac{27}{25}x


Gain= \inline (\frac{27}{25}x-\frac{9}{10}x)=\frac{9}{50}x


Hence gain% = \inline (\frac{9x}{50}\times \frac{10}{9x}\times 100) = 20%

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6 6289
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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4 6249
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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7 6189
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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4 6187