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:

If 25% of three-seventh of 26% of a number is 145.5, what is the number?

A) 4987 B) 5784
C) 5223 D) 4741
 
Answer & Explanation Answer: C) 5223

Explanation:

Given, 

 

25% of three-seventh of 26% of a number is 145.5

 

Let the required number be 'N'

 

i.e, 25100x37x26100xN = 145.5

 

N = 145.5x7x1000075x26

 

=> N = 5223.07

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9 7070
Q:

In an election between two candidates K and L, the number of valid votes received by K exceeds those received by L by 15% of the total number of votes polled. If 20% of the votes polled were invalid and a total of 8720 votes were polled, then how many valid votes did L get ?

A) 3241 B) 2457
C) 2642 D) 2834
 
Answer & Explanation Answer: D) 2834

Explanation:

Let the total number of votes polled in the election be 100k.
Number of valid votes = 100k - 20% (100k) = 80k
Let the number of votes polled in favour of K and L be a and b respectively.
a - b = 15% (100k) => a = b + 15k
=> a + b = b + 15k + b
Now, 2b + 15k = 80k and hence b = 32.5k
It is given that 100k = 8720
32.5k = 32.5k/100k x 8720 = 2834

The number of valid votes polled in favour of L is 2834.

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7 7038
Q:

A earns 50% of B's salary, B earns 80% of C's salary. If the total earnings for a month is Rs. 22000, then what is the earning for A ?

A) Rs. 4000 B) Rs. 4200
C) Rs. 4400 D) Rs. 4600
 
Answer & Explanation Answer: A) Rs. 4000

Explanation:

Let C's salary be Rs. x

Then B's salary = 80x/100

=> A's salary = (50/100) * (80x/100) = 40x/100

But given total earnings in a month = 22000

=> x + 80x/100 + 40x/100 = 22000

=> x + 120x/100 = 22000

=> x = 10000

=> A's salary = 40 x 10000/100 = Rs. 4000 

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10 7014
Q:

In a college, number of boys is 75% of number of girls. Difference between boys and girls is 35. On a particular day 20% boys were absent, then find the number of boys those who present?

A) 72 B) 84
C) 93 D) 81
 
Answer & Explanation Answer: B) 84

Explanation:

Ratio of girls and boys = 100% : 75% = 4:3

Difference is 1 unit = 35

So, 3 units = 35 x 3 = 105

If 20% absent, that’s mean 80% present.

So, present boys = 80% of 105 = 80×105100 = 84

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18 6846
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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5 6811
Q:

In order to maximize his gain, a shopping mall owner decides to reduce the price of electronics goods by 20% and as a result of this, the sales of electronics increase by 40%. If, as a result of these changes, he is able to increase his weekly collection by Rs. 1,05,000, find by what value did the gross collection increase per day?

A) Rs. 14400 B) Rs. 14600
C) Rs. 14800 D) Rs. 15000
 
Answer & Explanation Answer: D) Rs. 15000

Explanation:

It won't requires that much solving.

Here given the increase in weekly collection by Rs. 1,05,000

That is this increase denotes for all 7 days.

=> Gross Collection increase per day = Rs. 1,05,0007 = Rs. 15,000

Hence, the gross collection increase per day = Rs. 15,000.

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8 6797
Q:

If A is 40% less than B, then B is how much percentage more than A?

 

 

A) 72.33 B) 60
C) 40 D) 66.66
 
Answer & Explanation Answer: D) 66.66

Explanation:
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1 6787
Q:

The CO2 emissions in million metric tons over 3 years are given in the following table.

 

What is the increase in the percentage of CO2 emission from year 2016 to 2017?

A) 36.36% B) 26.36%
C) 63.63% D) 36.45%
 
Answer & Explanation Answer: A) 36.36%

Explanation:
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1 6781