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 payment per hour for a daily-wages employee is increased by 33.33 and the working time is reduced by 33.33%. What is the percentage change in the employee's income ?

A) 11.11% decrease B) 21.11% increase
C) 11.11% increase D) 21.11% decrease
 
Answer & Explanation Answer: A) 11.11% decrease

Explanation:

If earlier he is getting Rs. 1  per hr and working for 1 hr, income = Rs. 1
Now he is getting Rs 1.3333 per hr and working for 0.66667 hrs

Then income for 0.66667 hrs = Rs. 0.8889.

If payment per hr is increased by 33.33 %  and working hours dereased by 33.33%, then 11.11 % decrease in income.

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3 5645
Q:

4 45 of 259.99 = ? % of 1247.9

A) 96 B) 100
C) 78 D) 88
 
Answer & Explanation Answer: B) 100

Explanation:

Given 

4 45 of 259.99 = ? % of 1247.9

24/5 x 260 = ? x 1248/100

? = 1248 x 100/1248

? = 100.

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6 5617
Q:

Sneha’s weight is 140% of Veena’s weight. Rina’s weight is 90% of Sana’s weight. Sana weighs twice as much as Veena. If Sneha’s weight is x% of Rina’s weight, then x is equal to:

A) 596/9 B) 605/9
C) 645/9 D) 700/9
 
Answer & Explanation Answer: D) 700/9

Explanation:

Let Veena's weight = 1 kg

Sana's weight = 2 kg

Sneha's weight = 1.4 kg

Rina's weight = 1.8 kg

Now,according to the given data in the question,

1.8x100 = 1.4

 

x = 1.4 × 1001.8 = 7009 = 77 79.

 

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8 5508
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 5486
Q:

When the price of rice decrease by 10%, a girl could buy 1 kg more for Rs. 270. Then, the original price of the rice per kg is

A) Rs. 36 B) Rs. 30
C) Rs. 28 D) Rs. 40
 
Answer & Explanation Answer: B) Rs. 30

Explanation:

From the given data,

When the price of rice is decreased by 10%, the value of Rs. 270 would become

270 x 100/90 = 300

Now, the value 270 becomes 300

And given, the girl could buy 1 kg extra for that value

Change in value = 300 - 270 = Rs. 30

 

Therefore, 1 kg extra rice she can get for Rs. 30

 

=> The original price of rice = Rs. 30/kg.

 

As she gets only 9 kgs for Rs. 270 before 10% discount, now after discount she gets 10 kgs instead of 9 kgs for Rs. 270.  

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27 5462
Q:

A girl read 2/5 part of a book in 1st day, 34% in second day and remaining page in next two days. In two days she read equal number of page. If she read 52 pages on last day, then find out how many pages did the book contain?

A) 400 B) 376
C) 382 D) 356
 
Answer & Explanation Answer: A) 400

Explanation:

1st day the girl read = 40%

2nd day she read = 34 %

Remaining percentage of book = 100% - (40% +34%) = 26%

But given last two days she read equal number of pages

=> Each day she read 26%/2 = 13%

Last day she read 52 pages = 13%

13% = 52

1% = 4

=> 100% = 400

Total pages in the book is 400.

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12 5449
Q:

A shopkeeper’s earning increases by 25% in first year but decreases by 4% in the next and so on. After 5 years his total earnings would be Rs. 72,000. What is his present earning?

A) Rs. 40,000 B) Rs. 45,000
C) Rs. 42,000 D) Rs. 46,000
 
Answer & Explanation Answer: A) Rs. 40,000

Explanation:

Let his present earnings be Rs. p

ATQ,

(125/100) x (96/100) x (125/100) x (96/100) x (125/100) x p = 72000

p = Rs. 40,000.

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27 5448
Q:

A user type a content on 20 sheets, each sheet consist of 55 lines, and each line can have 66 characters. The content is again retyped on another set of sheets, these new sheets have 65 lines and each line can take 70 characters. Calculate the reduction in sheets ?

A) 2 or 60% B) 4 or 20%
C) 6 or 10% D) 8 or 5%
 
Answer & Explanation Answer: B) 4 or 20%

Explanation:

20 x 55 x 66 = L x 65 x 70
Here L = 72,600/4550 = 15.95 =~ 16
Reduction is 20-16 = 4

which is 20% reduction.

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3 5412