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 batsman scored 180 runs which included 11 boundaries and 8 sixes. What percent of his total score did he make by running between the wickets ?

A) 62.45% B) 51.42%
C) 48.88% D) 47.32%
 
Answer & Explanation Answer: C) 48.88%

Explanation:

Number of runs made by running = 180 - (11 x 4 + 8 x 6)
= 180 - (92)
= 88
Now, we need to calculate 88 is what percent of 180.
88180×100  = 48.888%.

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5 3922
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) 550 B) 575
C) 625 D) 700
 
Answer & Explanation Answer: D) 700

Explanation:

Let number of boys = B

Number of girls = G

From the given data,

1B/3 + 1G/2 = 300

But given B/3 = 100

=> B = 300

G/2 = 300 - 100

G = 200 x 2

=> G = 400

Therefore, total number of students in the college = B + G = 700.

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10 3906
Q:

Rohan spends 24% of an amount of money on an insurance policy, 34% on food, 19% on children’s education and 17% on recreation. He deposits the remaining amount of Rs. 540 in bank. How much total amount does he spend on food and insurance policy together?

A) Rs. 6350 B) Rs. 5220
C) Rs. 5890 D) Rs. 6458
 
Answer & Explanation Answer: B) Rs. 5220

Explanation:

Remaining % of amount with Rohan

= 100 - (24 + 34 + 17 + 19)

= 100 - 94

= 6%

=> 6% = 540

=> 100% = ?

540 x 100/6 = Rs. 9000

Now, Money spent on insurance and food is

= 34 + 24 = 58% of 9000

= 58 x 9000/100

= 58 x 90

= Rs. 5220

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5 3904
Q:

A seller charges 28% more from a customer as GST on an article. If customer paid Rs. 4544, what is the cost price of the article?

A) Rs. 3550 B) Rs. 2650
C) Rs. 3840 D) Rs. 2450
 
Answer & Explanation Answer: A) Rs. 3550

Explanation:

Let the cost price of the article be 'P'

Then from given data,

P + 28P100 = 4544=> 128P = 454400=> P = 3550

Hence, the cost price of the article = P = Rs. 3550

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15 3896
Q:

The population of a city is 415600.It increased by 25% in the first year and decreased by 30% in the second year.What is the population of the city at the end of second year?

Answer

As per given data, P = 415600, R1= 25% incresed, R2 = 30% decreased


Population of the city at the end of the second year= 



363650.

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12 3813
Q:

125% as a Fraction?

A) 1/4 B) 3/4
C) 5/4 D) 7/4
 
Answer & Explanation Answer: C) 5/4

Explanation:

Literally any percentage means divide by 100.

So 125% = 125100. That can be reduced to 5/4.

To convert to a decimal, you can do long division, dividing 5 into 4.

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5 3688
Q:

A person purchase 50 mangoes he sells 10 at 20% profit, 20 at 30% profit and rest got rotten. Find its total loss or profit%?

A) 28% B) 26%
C) 24% D) 22%
 
Answer & Explanation Answer: C) 24%

Explanation:

Let the cost price of each mango be Rs. 1

So 50 mangoes costs = Rs. 50

20% Profit on Selling Price of 10 mangoes = Rs. 12 

30% Profit on Selling Price of 20 mangoes = Rs. 26

Total = Rs. 38

Loss = 50 - 38 = 12

 

Loss% = (12/50) x 100 = 24%.

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5 3625
Q:

The percentage of metals in a mine of zinc ore is 60%. Now the percentage of silver is 3/4% of metals and the rest is zinc. If the mass of ore extracted from the mine is 8000 kg, the mass (in kg) of zinc is

A) 5147 kg B) 4764 kg
C) 3587 kg D) 2125 kg
 
Answer & Explanation Answer: B) 4764 kg

Explanation:

Mass of zinc ore = 8000 kg


Mass of metal = 60% of 8000 = 4800 kg


Mass of silver in metal = 3/4 x 4800/100 = 36 kg


Mass of zinc = 4800 - 36 = 4764 kg.

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6 3623