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 Shepherd had n goats in the year 2000. In 2001 the no.of goats increased by 40% . In 2002 the no. of goats declined to 70%. In 2003 the no. of  goats grew by 30%. In 2004, he sold 10% goats, then he had only 34,398 goats. The percentage increase of the no.of goats in this duration was:

A) 14.66% B) 16.66%
C) 20% D) 33.33%
 
Answer & Explanation Answer: A) 14.66%

Explanation:

There is no need to use the no of goats i.e (34,398). let initially thete be 1000 goats then 

 

  1000 -----> 1400 -----> 980 -----> 1274 ----->1146.6

 

Thus the % increase = (1146.6-1000)/100 x 100= 14.66%

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7 9267
Q:

The value of a machine depreciates at the rate of 10% every year. It was purchased 3 years ago. If its present value is Rs. 8,748, its purchase price was ?

A) Rs.14,000 B) Rs.12,000
C) Rs. 12,800 D) Rs. 15,000
 
Answer & Explanation Answer: B) Rs.12,000

Explanation:

We have P = 8748, R = -10 and n = 3
Therefore, the purchase price of the machine
= P1+R100n= 87481-101003
= 8748 x (100/90) x (100/90) x (100/90)
= 12,000.

 

Therefore, the purchase price of the machine was Rs. 12,000.

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7 9136
Q:

In an election, there were two candidates only. The candidate who got 62% of the total votes polled and was elected by a majority of 192 votes. The total number of votes polled was?

Answer

Suppose total votes polled is x


\inline \Rightarrow \inline \frac{62x}{100}=\frac{38x}{100}+192


\inline \Rightarrow \frac{62x}{100}-\frac{38x}{100}=192


\inline \Rightarrow \frac{24x}{100}=192\Rightarrow x=800

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Subject: Percentage

57 9036
Q:

What is better, to have 70% discount or 40 and 30% discount consequently ?

A) 40% is better B) 70% is better
C) Both are same D) None
 
Answer & Explanation Answer: B) 70% is better

Explanation:

Let Price be Rs.100

1st CASE:

Then 100 x 70/100 = 70
=> price after discount = 100-70 = Rs.30

2nd CASE:

Then 100 x 40/100 = 40
=> price after discount = 100-40 = Rs.60
then
60 x 30/100 = 18
=> price after 2 consequent discount = 60-18 = Rs.42

=>from 1 and 2 cases, 70% discount is better.

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10 8895
Q:

Each edge of a cube is increased by 20% then the percentage increase in surface area of the cube is : 

A) 144% B) 40%
C) 44% D) 72.8%
 
Answer & Explanation Answer: C) 44%

Explanation:

The surface area of a cube = 6a2 =  6 side2

 

New  Surface area = 6 x 1.44a2

 

Therefore, 0.44a2a2x100 = 44%

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13 8838
Q:

Rs. 69 were divided among 115 family members so that each lady gets 50 paise less than each gentleman, and each gentleman received twice the paise as each lady received. Find the number of  gentlemen in the family?

A) 23 B) 92
C) 48 D) 52
 
Answer & Explanation Answer: A) 23

Explanation:

Total number of female members = 115

Let the number of males = x

Number of females = y

=> x + y = 115  ......(1)

According to the given data,

x + y(0.50) = 69 ......(2)

From (1) & (2), we get

0.5y = 46

=> y = 46 x 2 = 92

=> x = 115 - 92 = 23

 

Hence, required number of gentlemen in the family = x = 23.

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8 8413
Q:

Ramesh spent Rs. 38460 on the renovation of his home, Rs. 24468 on buying furniture and remaining 28% of the total amount he had as cash with him. What was the total amount ?

A) 87400 B) 92520
C) 88470 D) 90150
 
Answer & Explanation Answer: A) 87400

Explanation:

Let X be the total amount with Ramesh

Given 28% of X = Cash remaining

=> Amount spent = 72% of X = 38460 + 24468 = 62928

=> 72% of X = 62928

=>  X = ?

=> X = 87400

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9 8340
Q:

When the price of whear was increased by 32%, a family reduced its consumption in such a way that the expenditure on wheat was only 10% more than before. If 30 kg per month were consumed before, find the new monthly consumption of family?

A) 27 kgs B) 25 kgs
C) 24 kgs D) 21 kgs
 
Answer & Explanation Answer: B) 25 kgs

Explanation:

Initial wheat per kg cost be Rs. 100

Then, monthly expenditure of the family = 30 x 100 = 3000

After increase in cost,

Let P be new monthly consumption of family.

P x 132 = 110/100 x 3000

=> P = 25 kg.

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7 8308