Permutation and combination are one of the trickiest sections of the IBPS RRB numerical ability section. A lot of candidates get confused when it comes to solving permutation and combination questions. However, permutations and combinations are pretty simple once you know the right technique. If you want to get selected in IBPS RRB 2021, then you must ensure that you get good marks for IBPS RRB permutation and combination. In the following post, we would talk about how you can solve permutation and combination questions. So, without much further ado, let’s begin learning.
Understanding IBPS RRB Permutation and Combination Questions
What are permutation and combination questions?
Permutation and combination basically ask you about the number of possible combinations. For example, you can get questions like ‘if five people are sitting at a table, they can be seated in how many ways?’
How many questions come in the exam?
Questions from permutations and combinations are quite common in IBPS RRB. Every year, there are about 5-6 questions asked from this one particular section. So, you should be prepared well.
What is the difficulty level?
The difficulty level of the questions varies from year to year. There are different types of questions asked in the examination and they have different levels of difficulties. On the whole, the difficulty of the questions varies from easy to moderate difficulty. However, in some years, you have the chance of getting difficult questions as well.
Do I need to learn the formulas?
Here is the thing – some of the most common questions asked in the IBPS RRB exam can be solved without using any formulas. However, that doesn’t mean that you would skip learning the formulas. Formulas are important and hence, you need to learn and memorize them. You don’t have to learn all of them. Just learn the basic formulas and that would be good enough for IBPS RRB exam.
Solving Some Common IBPS RRB Permutation and Combination Questions
Let us see how you can solve some of the most common types of questions in IBPS RRB questions. We would be using fewer formulas. Instead of using formulas, we would be using some basic concepts and logic. This would make solving the questions easier for everyone and also quicker. So, let’s begin.
Example 1 – 5 men in 5 chairs
Question: There are 5 men sitting at a table. In how many ways could the 5 men sit together at the table?
Solution: This is a permutation question. The easiest thing that you can do is take each chair at a time.
- First chair – In case of the first chair, you need to pick one. You can choose one of the 5 candidates. You can do that in 5 ways.
- Second chair – In case of the second chair, you again need to pick one. You are now left with 4 candidates. You can do that in 4 ways.
Repeat that for all for remaining chairs.
Now the total number of ways = 5(for the first chair)x 4x 3x2x1 or 5!
Total number of ways is 120
Answer: 120 ways.
Note that if the number of chairs is less, then we would only repeat the process ‘n’ number of times for ‘n’ number of chairs.
Let us look at an example for combination questions.
Example: Forming of committees
Question: The cricket board president has selected five members – Kapil, Sunil, Bishan, Ravi, and Sandip, for a three-member selection. In how many ways can the committee of three be formed from the five members?
Solution: The basic difference between permutation and combination is that in combination, the order doesn’t matter. We only need to know whether some is actually ‘in’ or ‘out’.
In solving these type of questions, we need to first find out the ways using the method learned for permutation.
So, we have a number of ways =5x4x3 (since only three members can sit in the committee)=60 ways
However, in these 60 ways, we have also included ways where the exactly the same members are selected. So, we need to omit them. Because we are only concerned about which members are selected not the order in which they are selected.
To omit them, we need to divide the total number of ways with n!, where n is the total numbers of members in the committee.
So, in this case, we have 3!=6
So, the number of ways in which a committee of three can be formed is =60/6=10 ways
The types of questions mentioned above are the most common types of questions. You can at least 2-3 questions of these type in your IBPS RRB 2018 exam. Let us now practice a little bit on these questions.
Question 1: In how many ways a group of 7 men can be seated at a table?
Question 2: In how many ways a committee of 5 men can be formed from a group of 7 men?
So, these were some of the ways in which you can solve IBPS RRB permutation and combination questions. Hope this article would help you in your RRB exam preparation. For more such amazing materials, keep browsing our website.
Best of luck!