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 girl want to read a complete book. She read 2/5 part of a book on 1st day, 34% on second day and remaining pages in next two days. On those two days she read equal number of pages. If she read 52 pages on last day, then find out total number of pages that the book contain ?

A) 400 B) 525
C) 325 D) 475
 
Answer & Explanation Answer: A) 400

Explanation:

Let the total number of pages in the book be 'x'.

From given data,

2x/5 + 34x/100 + 52 + 52 = x

 => 40x + 34x + 10400 = 100x

 => 26x = 10400

 => x = 400.

 Hence, total pages in the book are 400.

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7 5235
Q:

80% of 900 + 162 x 4 x ? = 113 - 99

A) 0.5 B) 1
C) 4 D) 0
 
Answer & Explanation Answer: A) 0.5

Explanation:

80x900/100 + 256 x 4 x ? = 1331 - 99

720 + 1024 x ? = 1232

? = 1232 - 720/1024

? = 512/1024 = 0.5

? = 0.5 

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11 5149
Q:

Prasanna invested certain amount in three different schemes X, Y and Z with the rate of interest 10% p.a, 12% p.a and 15% p.a respectively. If the total interest accrued in one year was Rs. 3200 and the amount invested in Scheme Z was 150% of the amount invested in Scheme X and 240% of the amount invested in Scheme Y, what was the amount invested in Scheme Y by Prasanna ?

A) Rs.6000 B) Rs.4500
C) Rs.7500 D) Rs.5000
 
Answer & Explanation Answer: D) Rs.5000

Explanation:

Let a, b and c be the amounts invested in schemes X, Y and Z respectively. Then,

As we know:

Simple interest (S.I.) = PTR/100

(a × 10 × 1/100) + (b × 12 × 1/100) + (c × 15 × 1/100) = 3200

= 10a + 12b + 15c = 320000 .........(1)

Now, c = 240% of b = 12b/5 .........(2)

And, c = 150% of a = 3a/2 => a = 2/3 c = (2 × 12)b/(3 × 5) = 8b/5 .......(3)

From (1), (2) and (3), we have

16b + 12b + 36b = 320000 => 64b = 320000 => b = 5000

∴ Sum invested in Scheme Y = Rs.5000.

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9 5145
Q:

The payment per hour for a daily-wages employee is increased by 33.33 and the working time is reduced by 33.33%. What is the percentage change in the employee's income ?

A) 11.11% decrease B) 21.11% increase
C) 11.11% increase D) 21.11% decrease
 
Answer & Explanation Answer: A) 11.11% decrease

Explanation:

If earlier he is getting Rs. 1  per hr and working for 1 hr, income = Rs. 1
Now he is getting Rs 1.3333 per hr and working for 0.66667 hrs

Then income for 0.66667 hrs = Rs. 0.8889.

If payment per hr is increased by 33.33 %  and working hours dereased by 33.33%, then 11.11 % decrease in income.

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3 4992
Q:

If there are 150 questions in a 3 hr examination. Among these questions 50 are type A problems, which requires twice as much as time be spent on the rest of the type B problems. How many minutes should be spent on type A problems ?

A) 75 min B) 82 min
C) 90 min D) 101 min
 
Answer & Explanation Answer: C) 90 min

Explanation:

Let X = Time taken for each of Type B Problems(100 Problems)
And 2X = Time taken for each of Type A problems(50 problems)

Total time period = 3hrs = 3 x 60min = 180 minutes

100X + 50(2X) = 180
100X + 100X = 180
200X = 180 min

X = 180/200
X = 0.90 min

By convertiing into seconds,

X = 0.90 x 60 seconds
X = 54 sec

So, time taken for Part A problems is = 54 x 2 x 50 = 5400 seconds
= 5400/60sec = 90 minutes.

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8 4968
Q:

4 45 of 259.99 = ? % of 1247.9

A) 96 B) 100
C) 78 D) 88
 
Answer & Explanation Answer: B) 100

Explanation:

Given 

4 45 of 259.99 = ? % of 1247.9

24/5 x 260 = ? x 1248/100

? = 1248 x 100/1248

? = 100.

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6 4951
Q:

In a hoel, 60% had vegetarian lunch while 30% had non-vegetaian lunch and 15% had both types of lunch. If 96 people were present, how many did not eat either type of lunch ?

A) 24 B) 30
C) 36 D) 42
 
Answer & Explanation Answer: A) 24

Explanation:

n (A) = (60/100 * 96) = 288/5, n (B) = (30/100 * 96) = 144/5, n (A ∩ B) = (15/100 * 96) = 72/5.

n(A ∪ B) = n (A) + n (B) - n (A ∩ B) = 72.

So, people who had either or both types of lunch = 72.

Hence, people who had neither type of lunch = (96 - 72)= 24.

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1 4852
Q:

Sneha’s weight is 140% of Veena’s weight. Rina’s weight is 90% of Sana’s weight. Sana weighs twice as much as Veena. If Sneha’s weight is x% of Rina’s weight, then x is equal to:

A) 596/9 B) 605/9
C) 645/9 D) 700/9
 
Answer & Explanation Answer: D) 700/9

Explanation:

Let Veena's weight = 1 kg

Sana's weight = 2 kg

Sneha's weight = 1.4 kg

Rina's weight = 1.8 kg

Now,according to the given data in the question,

1.8x100 = 1.4

 

x = 1.4 × 1001.8 = 7009 = 77 79.

 

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