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:

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:

15% of 60 is 45% of __

 

A) 20 B) 30
C) 180 D) 40
 
Answer & Explanation Answer: A) 20

Explanation:
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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 4592
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 4511
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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4 4483
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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2 4435
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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