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:

In a hostel the rent per room is increased by 20%. If number of rooms in the hostel is also increased by 20% and the hostel is always full, then what is the percentage change in the total collection at the cash counter?

A) 30% B) 40%
C) 44% D) 48%
 
Answer & Explanation Answer: C) 44%

Explanation:
Let initial rent be rs 10
And initial rooms be 10
So initial collection = 10*10 = Rs 100
Now new rent = 10 + 20% of 10 = 12
New no of rooms = 10 + 20% of 10 = 12
So new collection = 12*12 = 144
% change in collection = (144-100)/100*100 = 44%
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Q:

In a city of engineers of 4800, the number of female engineers are 3/8th of them. The number of female engineers is what percentage of the number of male engineers?

A) 76 B) 60
C) 56 D) 52
 
Answer & Explanation Answer: B) 60

Explanation:

Total engineers = 4800

Number of female engineers = 3/8 x 4800 = 1800

Then, number of male engineers = 4800 - 1800 = 3000

Now, required is female engineers is what percentage of the number of male engineers

=> 1800 is what % of 3000

=> p x 3000/100 = 1800

=> 30p = 1800

p = 60%

 

Hence, female engineers is 60 percentage of the number of male engineers.

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6 3819
Q:

In an election between two candidates, the winning candidate got 70% of the valid votes and won by a majority of 9000 votes. If out of total votes polled 90% votes are valid, then what is the total number of votes polled?

 

A) 30000 B)  25000
C) 22500 D) 27000
 
Answer & Explanation Answer: B)  25000

Explanation:
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29 3816
Q:

5% of 40,000 is

A) 20000 B) 2000
C) 200 D) 20
 
Answer & Explanation Answer: B) 2000

Explanation:

5% of 40,000  = 5100 × 40,000 = 5 × 400 = 2,000  

 

Hence, 5% of 40,000 = 2,000.

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7 3811
Q:

16 of 225 is =

A) 7.11 B) 7.21
C) 6.87 D) 7.58
 
Answer & Explanation Answer: A) 7.11

Explanation:

16 of 225 is = 

16 = p × 225100p = 1600225 = 7.1111

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9 3806
Q:

A man’s average monthly expenditure for the first four months of the year was Rs. 231.25. For the next five months, the average monthly expenditure was Rs. 22.75 more than what it was during the first four months. If the person spent Rs. 605 in all during the remaining three months of the year, find what percentage of his annual income of Rs. 3500 did he save in the year?

A) 10% B) 15%
C) 20% D) 25%
 
Answer & Explanation Answer: C) 20%

Explanation:

A man's average monthly expenditure for the first four months of the year = Rs.231.25.
For four month = 231.25 * 4 = Rs. 925
For next five month he spend = 231.25 + 22.75 for one month.
In five month he spend = (231.25 + 22.75) X 5 = 1270
If the person spent Rs. 605 in all during the remaining three months of the year,
Total expense = 925+1270+605= 2800
Saving = 3500-2800 = 700
% saving = 700/3500 * 100 = 20%

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Q:

If the side of square is increased by 6%, then what will be the percentage increase in its area?

A) 3.2 B) 12.04
C) 12.12 D) 12.36
 
Answer & Explanation Answer: D) 12.36

Explanation:
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2 3746
Q:

Suresh starts working as a analyst on an annual salary of Rs. 160000. If he receives a 15% pay-rise each year, the number of years he has worked for the company, when his annual salary became Rs. 279841 is

A) 3.5 yrs B) 4 yrs
C) 4.5 yrs D) 5 yrs
 
Answer & Explanation Answer: B) 4 yrs

Explanation:

From the given data in the question,

279841 = 160000 x 1+15100t279841160000 = 115100t

t = 4 years.

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6 3724