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:

74.99% of 1299 + 8.98% of 1899 = ? 

A) 1378 B) 1301
C) 1212 D) 1197
 
Answer & Explanation Answer: C) 1212

Explanation:

74.99% of 1299 + 8.98% of 1899 = ? 

? = 75 x 1400100 + 9 x 1800100 ? = 1050 + 162? = 1212.

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8 4387
Q:

In an election between two candidates 70% of the voters cast their votes, out of which 2% of the votes were declared invalid. A candidate got 7203 votes which was 60% of the total valid votes. Find the total number of voters enrolled in that election.

A) 18050 B) 17500
C) 17000 D) 7203
 
Answer & Explanation Answer: B) 17500

Explanation:

Let total number of votes enrolled = x
No. of voted cast = 70% of x = 0.7x
Valid votes = 98% of 0.7x
⇒ 60% of total valid votes = 7203 = 60% of 98% of 0.7x
⇒ 0.6 X 0.98 X 0.7x = 7203
⇒ x = 7203 / (0.6 X 0.98 X 0.7)
⇒ x = 17500

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1 4375
Q:

In a competitive examination, the average marks for the entire examination was 60 marks. If 20% of the applicants scored 85 marks and 25% scored 95 marks. What was the average marks of the remaining applicants in the examination ?

A) 60 B) 52
C) 45 D) 35
 
Answer & Explanation Answer: D) 35

Explanation:

Let the total applicants be 100

 

Then, 20% got 85 marks

i.e 20 x 85 = 1700

 

and 25% got 95 marks

 i.e 25 x 95 = 2375

 

Now, the remaining applicants are 55 and let the average marks scored by them be x.

 

Therefore, 2375 + 1700 + 55x  =  60×100 

6000 - 4075 = 55x

55x=1925

x=35.

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8 4348
Q:

If the price of diesel increases by 25% and Karthik intends to spend only an additional 15% on diesel, by how much % will he reduce the quantity of diesel purchased ?

A) 6.67 % B) 8 %
C) 7.41 % D) 9 %
 
Answer & Explanation Answer: B) 8 %

Explanation:

Let the price of 1 litre of diesel be Rs.x and let Karthik initially buy 'y' litres of diesel.
Therefore, he would have spent Rs. xy on diesel.

When the price of diesel increases by 25%, the new price per litre of diesel is 1.25x.

Karthik intends to increase the amount he spends on diesel by 15%.
i.e., he is willing to spend xy + 15% of xy = 1.15xy

Let the new quantity of diesel that he can get be 'q'.
Then, 1.25x x q = 1.15xy
Or q = (1.15/1.25)y = 0.92y.

As the new quantity that he can buy is 0.92y, he gets 0.08y lesser than what he used to get earlier.

Or a reduction of 8%.

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5 4343
Q:

40% of 80?

A) 36 B) 32
C) 42 D) 44
 
Answer & Explanation Answer: B) 32

Explanation:

Here 40% of 80 is given as

40100 x 80 = 8 x 4 = 32

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7 4329
Q:

75% of 450 + ? % of 560 = 600 

A) 52.385 B) 46.875
C) 42.155 D) 40.555
 
Answer & Explanation Answer: B) 46.875

Explanation:

75% of 450 + ? % of 560 = 600 

75 x 450100 + ? x 560100 = 60075 x 92 + 28p5 = 60075x9x5 + 56p10 = 6003375 + 56p = 600056p = 2625p = 46.875

 

Hence, in the given question ? = 46.875

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3 4251
Q:

Madhu got 32% of the maximum marks in a Bank examination and failed by 8 marks. However, Kumar who took the same examination got 42% of the total marks and got 16 marks more than the cut-off marks. What was the cut-off marks in the examination ?

A) 76.8 B) 86.8
C) 78.8 D) 84.8
 
Answer & Explanation Answer: D) 84.8

Explanation:

Let 'M' be the maximum marks in the examination.

Therefore, Madhu got 32% of M = 32M/100 = 0.32M
And Kumar got 42% of M = 42M/100 = 0.42M.
In terms of the maximum marks Kumar got 0.42M - 0.32M = 0.1M more than Madhu. ---- (1)

The problem however, states that Kumar got 16 marks more than the cut-off mark and Madhu got 8 marks less than the cut-off mark. Therefore, Kumar has got 16 + 8 = 24 marks more than Madhu. ---- (2)

Now, Equating (1) and (2), we get
0.1M = 24 => M = 24/0.1 = 240
'M' is the maximum mark and is equal to 240 marks.
We know that Madhu got 32% of the maximum marks.
Therefore, Madhu got 32 x 240/100 = 76.8 marks.
We also know that Madhu got 8 marks less than the cut-off marks.

Therefore, the cut-off marks will be 8 marks more than what Madhu got
= 76.8 + 8 = 84.8.

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11 4248
Q:

60 percent of 2/7 of three-fourth of a number is 2664. What is the number ?

A) 20720 B) 21352
C) 25421 D) 24150
 
Answer & Explanation Answer: A) 20720

Explanation:

Let N be the required number. 

=> 60100x27x34xN=2664  

=> N = 2664x2x7x5/9  

=> N = 20720.

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