In view of the coronavirus pandemic, we are making LIVE CLASSES and VIDEO CLASSES completely FREE to prevent interruption in studies
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. 

Suggested Videos

Play
Play
Play
Arrow
Arrow
ArrowArrow
Area of Triangles
Coin Toss
VST Permutations and Combinations Problem 1 and its Solution
Slider

 

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

Share with friends

Customize your course in 30 seconds

Which class are you in?
5th
6th
7th
8th
9th
10th
11th
12th
Get ready for all-new Live Classes!
Now learn Live with India's best teachers. Join courses with the best schedule and enjoy fun and interactive classes.
tutor
tutor
Ashhar Firdausi
IIT Roorkee
Biology
tutor
tutor
Dr. Nazma Shaik
VTU
Chemistry
tutor
tutor
Gaurav Tiwari
APJAKTU
Physics
Get Started

6
Leave a Reply

avatar
5 Comment threads
1 Thread replies
0 Followers
 
Most reacted comment
Hottest comment thread
6 Comment authors
Ayushi shuklaHoneypavan kalyanPriyaanmol Recent comment authors
  Subscribe  
newest oldest most voted
Notify of
Jagdish
Guest
Jagdish

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
mahu

ook

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

pavan kalyan
Guest
pavan kalyan

1 5 20 ???

lavanya lakhotia
Guest
lavanya lakhotia

60

srashti
Guest
srashti

60

Honey
Guest
Honey

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

Ayushi shukla
Guest
Ayushi shukla

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

Stuck with a

Question Mark?

Have a doubt at 3 am? Our experts are available 24x7. Connect with a tutor instantly and get your concepts cleared in less than 3 steps.
toppr Code

chance to win a

study tour
to ISRO

Download the App

Watch lectures, practise questions and take tests on the go.

Get Question Papers of Last 10 Years

Which class are you in?
No thanks.