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:

Kalyan purchased a Maruti van for Rs. 1,96,000 and the rate of depreciation is 14(2/7) % per annum. Find the value of the van after two years ?

A) Rs. 1,24,000 B) Rs. 1,44,000
C) Rs. 1,32,000 D) Rs. 1,62,000
 
Answer & Explanation Answer: B) Rs. 1,44,000

Explanation:

Value of Maruti Van, V1 = Rs. 1,96,000
Rate of depreciation, r = 14(2/7)% = 100/7%; Time, t = 2 years
Let V2 is the value after depreciation.

V2 = V11 - r100t
V2 = 196001 - 10071002

V2 = 196000(6/7)(6/7)

V2 = (196000x36)/49 = Rs. 1,44,000.

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4 6701
Q:

One-third of the boys and one-half of the girls of a college participated in a sport. If the number of participating students is 300, out of which 100 are boys. What is the total number of students in the college?

A) 500 B) 300
C) 600 D) 700
 
Answer & Explanation Answer: D) 700

Explanation:

Let number of boys in the school = x

Let number of girls in the school = y

Number of students participated in the sports = 300

Out of which boys = 100

but given number of boys participated in sports = x/3

=> x/3 = 100

=> x = 300

Remaining girls = 300 - 100 = 200

=> y/2 = 200

=> y = 400

Therefore, total number of students in the school = x + y = 300 + 400 = 700

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14 6603
Q:

Subbu purchased a tape recorder at 9/10 of its selling price and sold it at 8% more than its selling price. His gain is

Answer

Let S.P = x then C.P = \inline \frac{9x}{10}


Selling price received by subbu = (108% of x)


                                            = \inline \frac{108}{100}x=\frac{27}{25}x


Gain= \inline (\frac{27}{25}x-\frac{9}{10}x)=\frac{9}{50}x


Hence gain% = \inline (\frac{9x}{50}\times \frac{10}{9x}\times 100) = 20%

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Subject: Percentage

6 6592
Q:

Express 6.72 % in ratio ?

A) 65 : 124 B) 42 : 625
C) 21 : 125 D) 37 : 442
 
Answer & Explanation Answer: B) 42 : 625

Explanation:

6.72/100 = 672/10000 = 42/625

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10 6586
Q:

A restaurant offers a new promotion of 20% off the original price of cakes, which is Rs. 12. Before the promotion 250 cakes were sold each day. After the promotion, the sale of cakes increases an average of 18% more per day. How much more or less does the restaurant make each day in cakes sales after the promotion?

A) Rs. 185 less B) Rs. 202 more
C) Rs. 175 more D) Rs. 168 less
 
Answer & Explanation Answer: D) Rs. 168 less

Explanation:

Cost of each cake P1 & P2 = Rs. 12

Offer decrease in % = 20%

Increase in sale per day (Q2) = 250 - 18%

Total quantity per day (Q1) = 250

Hence, required change total revenue

TR = P2Q2 - P1Q1 = (12 x 0.8 x 250 x 1.18) -  (12 x 250) = - Rs.168.

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15 6564
Q:

3 is what percent of 5?

A) 45% B) 60%
C) 72% D) 80%
 
Answer & Explanation Answer: B) 60%

Explanation:

Here it is asked that 3 is what percent of 5

Let 3 is K percent of 5.

=> K x 5/100 = 3

=> K = 300/5 = 60

 

Hence, 3 is 60% of 5.

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8 6520
Q:

Last year vivek saved 10% of his annual earnings, this year he earned 5% more than last year and he saved 12% of his annual earnings. The amount saved this year was what percentage of the amount saved last year ?

A) 87% B) 98%
C) 138% D) 126%
 
Answer & Explanation Answer: D) 126%

Explanation:

Suppose total earnings = Rs. 10000
10% saving = 10000 x (10/100) = Rs. 1000
This year 5% more income than prev year = Rs. 10500
12% saving = 10500 x (12/100) = Rs. 1260
Percentage of amount saved = (1260/1000) x 100 = 126%

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4 6431
Q:

Twelve percent of Kalyan's monthly salary is equal to the sixteen per cent of Nandu's monthly salary. Sarnesh's monthly salary is half that of Nandu's monthly salary. If sarnesh's annual salary is Rs. 1.08 lacs, What is Kalyan's monthly salary ?

A) 15,000 B) 36,000
C) 24,000 D) 12,500
 
Answer & Explanation Answer: C) 24,000

Explanation:

Let K = Kalyan's monthly salary
N = Nandu's monthly salary
S = Sarnesh's monthly salary.
Then from given data,
12% of K = 16% of N
S = N/2 => N = 2S
K = 16/12 x N = 16/12 x 2S
= 16/6 x 1.08/12 = 16/6 x 0.09 = 0.24 lacs = 24,000

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4 6299