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:

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:

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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Q:

In an examination a candidate got 30% marks and failed by 30 marks. If the passing marks are 60% of the total marks, then the maximum marks will be: 

A) 450 B) 600
C) 300 D) 100
 
Answer & Explanation Answer: D) 100

Explanation:

Passing marks are 0.6x 

 

so 0.3x + 30 = 0.6x   => x = 100

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19 13435
Q:

A dress on sale in a shop is marked at $D. During the discount sale its price is reduced by 15%. Staff are allowed a further 10% reduction on the discounted price. If a staff member buys the dress what will she have to pay in terms of D ?

A) 0.75D B) 0.76D
C) 0.765D D) None of the above
 
Answer & Explanation Answer: C) 0.765D

Explanation:

If the price is reduced by 15 %, then the new price will be 0.85D

If this new price is further reduced by 10%, the discounted price will be 0.9 x 0.85D = 0.765D

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12 13299
Q:

What should come in place of question mark (?) in the following question?

45% of 400+ √? = 56% of 750 - 40% of 350

A) 10000 B) 1000
C) 10201 D) 9801
 
Answer & Explanation Answer: A) 10000

Explanation:

45/100×400+√?=56/100 ×750 -40/100 ×350

180 + √? = 420 - 140 180 + √? = 280 √? = 280 - 180 √? = 100 ? = 1002 ? = 10000

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Q:

In a factory there are three types of Machines M1 , M2 and M3 which produces 25%, 35% and 40% of the total products respectively. M1, M2 and M3 produces 2% , 4% and 5% defective products, respectively. What is the percentage of non-defective products?

A) 89% B) 97.1%
C) 96.1% D) 86.1%
 
Answer & Explanation Answer: C) 96.1%

Explanation:

Non- defective products

 

25x0.98+35x0.96+40x0.95100 x 100 = 96.1

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22 13203
Q:

A number, when 35 is subtracted from it, reduces to its 80 percent. What is four - fifth of that number  ?

A) 175 B) 140
C) 135 D) 95
 
Answer & Explanation Answer: B) 140

Explanation:

x - 35 = 80x/100 

=> x = 175 

=> 4x/5 = 4x175/5 = 140.

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Q:

If price of rice increased by 25%, so that a man is can able to purchase 5 kg less rice in Rs. 500. Find the original price of rice per kg ?

A) Rs. 20 B) Rs. 24
C) Rs. 26 D) Rs. 29
 
Answer & Explanation Answer: A) Rs. 20

Explanation:

Let the original price of rice be Rs. x

Let rice a man can buy for Rs. 500 at rs. x/kg be = R kgs

From given data, for Rs. 500

x ---- R kgs

(x + 25x/100) ---- (R - 5) kgs

=> Rx = (R - 5)(x + 25x/100)

=> Rx = (R - 5)(125x/100)

=> 100Rx = 125Rx - 625x

=> R = 25

So at rate of Rs. x/kg, man get 25 kgs for Rs. 500

=> x = 500/25 = Rs. 20

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