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:

Which value is equal to 5% of 1,500?

A) 35 B) 55
C) 75 D) 45
 
Answer & Explanation Answer: C) 75

Explanation:

In the question it is asked for 5% of 1500

5 x 1500/100 = 15 x 5 = 75.

 

Hence, 5% of 1,500 is equal to 75.

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10 5791
Q:

A man spend 20% of his monthly salary on his children's education and 50% of his salary on food and transport. After Paying the rent of Rs.1000, he is left with Rs.2000. What is his monthly salary?

A) 7000 B) 10000
C) 14000 D) 20000
 
Answer & Explanation Answer: B) 10000

Explanation:

Let his monthly salary be 'P'

20% on children's education = 20P100 = P5

50% on food and transport = 50P100 = P2

1000 on rent

=> P - P5 - P2 - 1000 = 2000=> 3P = 30000=> P = 10000

 

Therefore, his monthly salary = Rs. 10,000

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4 5719
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 5668
Q:

In a school of 1500 boys, 35% are Hindu, 30% are Sikh,15% are Muslims and remainning are Christians. Find number of christian boys in the school ?

Answer

Given total number of boys in the school = 1500


In that 35% are Hindu, 30% are Sikh, 15% are Muslims


=> 35 + 30 + 15 = 80%


Remaining Boys = 100% - 80% = 20% of 1500


=> 20 x 1500/100 = 300 boys are Christians. 

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5 5634
Q:

A duster is of dimension 5x5x7 all in cms,  is sinked into a cylindrical vessel of radius 5 cm and height 10 cm. After insertion the level of the water is inccresed by 2.14 cm. Then by what percentage the part of the duster is above the layer ?

A) 96 % B) 4 %
C) 97 % D) 3 %
 
Answer & Explanation Answer: B) 4 %

Explanation:

Imension of the duster is assumed as 5x5x7 cm3

Volume of the duster below the water layer
= volume of water increased
= πxrxrxh = 3.14×52×2.14 ≈ 168 cm3

Total volume of the duster = 5×5×7 = 175 cm3

Percentage of the duster part below the layer = 168×100/175 = 96%

Percentage of the duster part above the layer = 4%

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4 5623
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 5600
Q:

12 as a percentage?

A) 50% B) 5%
C) 0.5% D) 0.05%
 
Answer & Explanation Answer: A) 50%

Explanation:

1/2 as a percentage means

1/2 = 0.5 in decimal

Now, in percentage means 0.5 x 100% = 50%.

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8 5590
Q:

A sales boy is allowed 412 % discount on the total sales made by him plus a bonus of 14% on the sales over Rs.12,000.If his total earnings were Rs.2400, then his total sales(in Rs.) are ?

A) Rs.60,145.23 B) Rs.54,285.54
C) Rs.52,147.85 D) Rs.50,589.47
 
Answer & Explanation Answer: D) Rs.50,589.47

Explanation:

Let the total earnings be Rs.x 

Then 412% of x + 14% of (x-12000) =2400

 92×x100+14×x-12000100=2400

=>  x=50,589.47

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8 5542