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:

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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Q:

100 percent of which number is 20?

A) 100 B) 500
C) 20 D) 0
 
Answer & Explanation Answer: C) 20

Explanation:

Let the rquired number be 'P'

According to the question,

100 x P100 = 20=> P = 20 x 100100 = 20

Hence, 100 percent of the number 20 is 20.

 

Now, you can also try for

20 percent of what number is 100

20 x P100 = 100=> P = 100 x 10020 = 500=> P = 500

Hence, 20 percent of the number 500 is 100.

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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 4692
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 4598
Q:

There are 1650 students in a college. The difference between the number of boys and girls in the college is 400. What is the percentage of girls in the college ?

A) 49 B) 34
C) 43 D) 38
 
Answer & Explanation Answer: D) 38

Explanation:

Let no. of boys be 'B' and no. of girls be 'G'

Here from given data,

B + G = 1650 .....(1)

B - G = 400 .....(2)

From (1) & (2), we get

2B = 2050

=> B = 1025

=> G = 1650 - 1025 = 625

Hence, the % of girls = 625 x 100/1650

=> 38% (approx).

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Q:

In a class of 80 students and 5 teachers, each student got sweets that are 15% of the total number of students and each teacher got sweets that are 25% of the total number of students. How many sweets were there?

A) 1060 B) 960
C) 860 D) 760
 
Answer & Explanation Answer: A) 1060

Explanation:

From the given data,

80 x 15/100 of 80 + 5 x 80 x 25/100

= 960 + 100

= 1060.

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Q:

Value of vehicle at end of each year depreciates at the rate of 3/5th of value at the beginning. If Initial value is 10,000Rs then at the end of three years its value is ? 

A) Rs. 6000 B) Rs. 3600
C) Rs. 2160 D) Rs. 415
 
Answer & Explanation Answer: C) Rs. 2160

Explanation:

End of first year     :  10000 x (3/5) = Rs. 6000
End of second year :  6000 x (3/5) = Rs. 3600
End of third year    :  3600 x (3/5) = Rs. 2160

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Q:

What is 85 of 352?

A) 21.5% B) 24.14%
C) 23.68% D) 25.47%
 
Answer & Explanation Answer: B) 24.14%

Explanation:

Here 85 of 352 => 85 is what percent in 352

Let p% of 352 is 85

Percentage(%) is generally calculated in the total of 100.

=> p x 352/100  = 85

=> p = 8500/352  = 24.14%

 

Hence, 85 is 24.14% of 352.

 

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