Number Series

Chain Rule

When two or more elements are given in a scenario than chain rule can be applied. There are two figures in each of these two elements. While one figure is missing in one of the elements. To find out this missing part of the figure we use the chain rule.  Suppose in the question, ‘days’ part is missing. Thus, you will compare ‘days’ with other elements independently to find out the element and ignore the other elements. Let us see chain rule examples. 

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Principles of the Chain Rule

chain rule examples

When you do the comparison there are mainly two principles that have to be followed:

  1. If the missing part is not greater than the given part than the numerator should also be small than the denominator. That is, it should be a/b < 1. Here a and b are the part given in the other elements.
  2. If the given part is smaller than the missing part, then the denominator should also be kept smaller than the numerator. Thus, it should be a/b > 1. Here also a and b are the given parts of the other element.

Chain Rule Examples

Some of the types of chain rule problems that are asked in the exam.

Question 1

In school, there are some chocolates for 240 adults and 400 children. If the chocolates are taken away by 300 children, then how many adults will be provided with the remaining chocolates?

Here it is clearly given that there are chocolates for 400 children and 300 of them has already taken the chocolates. So, the total remaining children that need to be provided with chocolates is 400 – 300, which is 100.

It is also given in the question that 400 children are equal to 240 adults. So, 1 child = 240/400 adults. Therefore, 100 children will be the same as 240/400 x 100 adults. This equals up to 60 adults. So, the required answer over here is 60 adults.

Learn more about Geometric Series here in detail.

Question 2

It takes 48 laborers to construct a house in 24 days. Find out the number of days that 36 laborers will take to build a house.

This is a case of indirect proportion. This means that less the number of people more will be the days taken by them. Suppose, the required number of days is ‘x’. So, the laborers and days here will be in ratio.

This will be 36: 48:: 24: x. Also, note that because of indirect proportion, 48/36 will be written as 36/48. So, x = 48 x 24/36 => 32. So the required number of days is 32.

Question 3

Suppose that a bike travels ‘a’ km in ‘b’ liters. Find the amount of petrol the bike requires for 7/2 of ‘a’ km.

Suppose the required amount of petrol to be found out is ‘X’ liters. The bike, in this case, uses ‘b’ liters to travel ‘a’ km. More the amount of traveling (km), more will be the petrol required (liters).

So, the ratio of petrol: the ratio of km. Thus, a : 7a/2 :: b : X. Therefore, 7ab/2a = 7b/2. So, the answer required is 7/2 liters of petrol.

Practice Questions

Q. A bus travels 11.25 km of the journey with 750 ml of fuel. Find the cost to travel 63.75 km of 1 liter of petrol is priced at Rs. 61.

A. 260                    B. 259.25                  C. 275.25                D. 260.25

Answer: B. 259.25

Q. It takes 6 days to complete 2/5th of the work. How many more days will it take to complete the work at this rate?

A. 6 days               B. 9 days                C. 12 days                 D. 15 days

Answer: B. 9 days

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Jagdish
Guest

5 7 31 283 ?

Parth Joshi
Guest
Parth Joshi

4533

ajay jadhav
Guest
ajay jadhav

3967

Priya
Guest
Priya

5×1+2=7
7×4+3=31
31×9+4=283
283×16+5=4533

mahu
Guest

ook

Venu
Guest
Venu

4533

anmol
Guest
anmol

4,8,24,28,84,88,_

Parth Joshi
Guest
Parth Joshi

264

Rahul
Guest
Rahul

4+4=8×3=24+4=28×3=84+4=88×3=264

Ashish
Guest
Ashish

84+100=184or 84+240=324

spy7
Guest
spy7

4+4=8
8×3=24
24+4=28
28×3=84
84+4=88
88×3=264

pavan kalyan
Guest
pavan kalyan

1 5 20 ???

lavanya lakhotia
Guest
lavanya lakhotia

60

anmol
Guest
anmol

1*3+2=5
5*3+5=20
20*3+7=67
can it not be like this???
if not then why?

Sathish
Guest

1×5=5
5×4=20
20×3=60

Saumit
Guest
Saumit

How

srashti
Guest
srashti

60

anmol
Guest
anmol

1*3+2=5
5*3+5=20
20*3+7=67
can it not be like this???
if not then why?

anmol
Guest
anmol

thats 20*3+8=68

Ashish
Guest
Ashish

1×2+3=5×3+5=20×4+7=86

Honey
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Honey

16,4,68,12,?,4,30,1,9 plz reply i need it

ABCD
Guest
ABCD

GAY

Ayushi shukla
Guest
Ayushi shukla

2,3,3,5,10,13,?,43,172,177

Sneha
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Sneha

4,5,5,7,9,13,10__,14

abcd
Guest
abcd

I think
Answer. 15
In series of odd numbers (4, 5,9,10,14) there is addition of 1 and 4 alternately.
And in series of even numbers (5, 7,13,?) There is addition of 2 and 6 alternately.

Janu
Guest
Janu

Find missing teams-1,5,14,?,44

Robin rathi
Guest
Robin rathi

Find the missing number of this series
60,50,60,90,41,_?

Options 1. 12
2. 18
3. 25
4. 30
5. none this above

Rohith
Guest
Rohith

26,4,20,10,14,16,8,22,2,28

Paulo
Guest

____,360,000,000,____, 389,000,000,____, 420,000,000

Sune Pedersen
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Sune Pedersen

37 52 93 75 29 ? what is the math behind this

Sonali sahu
Guest
Sonali sahu

2,1,0,-3,-24,? Find the next number

Pinky Choudhary
Guest

Upper line 3 5 8 mid line 6 10 32 lower line 9 ? 50 me missing no. Kya h

Akash
Guest
Akash

94 101 115 136 164 ?

Ashish
Guest
Ashish

199

Lokesh
Guest
Lokesh

QID : 426 – In the following question, select the
missing number from the given alternatives.
41, 83, 167, 335, 671, ?
Options:
1) 1297
2) 1343
3) 1447
4) 1661

Ashish
Guest
Ashish

1343

Shriya Nimje
Guest
Shriya Nimje

50,50,54,72,?,220

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