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Permutations and Combinations Tricks | RBI Grade B 2018

Permutations and Combinations Tricks SBI PO 2018 RBI Grade B 2018

Permutations and Combinations are an important topic in every banking examination. If you aspire to be an RBI Grade B Officeryou must have a strong understanding of the basics of mathematics, which includes permutations and combinations. Due to their relatively complex nature, students generally tend to avoid the Permutations and Combinations topic when studying for the bank PO examination. However, the topic can be dealt with relative ease if one can look at the kinds of questions that come or appear in the examination and prepare for them accordingly. There are four kinds of questions or rather 4 types of questions that can be asked from the permutations and combinations topic in the banking examinations. Each of the four types has been discussed below with the ways to solve the same. 

Permutations and Combinations Type 1 

In the first type, you will be required to determine the total number of words that can be created by rearranging the alphabets. For example, a simple example would be to look at the word ‘PEN’ and determine the total number of words that can be created by rearranging the alphabets. It is not mandatory that the words should have meanings, but rather they should still be words and they cannot be repeated (the same words cannot be created twice).

Consider the word, “WORLD”. What is the number of words (meaningful or meaningless) be created from the same? 

To solve this kind of questions, follow the steps:

  • Count the number of alphabets in the world. In this case, there are 5 alphabets in the word. 
  • Draw a table to count the number of times each letter appears in the world. 
  • Use the formula to determine the answer: 
    • No. of Words = Factorial of Total Number of Letters/Product of Factorial of Repetitions of Each Letter

Permutations and Combinations Type 2

The second kind of questions in the Permutations and Combinations topic happens to be an extension of the first kind. The only difference here is that in the case of the type 2 questions, you will be asked to determine the number of words you can create but with keeping 2 of the alphabets together. In this case, you must consider both the alphabets as a single one since they will always be together with each other. Once you do this, all other kinds shall be the same in terms of the methods used to solve them for example. 

Permutations and Combinations Type 3

The third kind of questions is quite common in the case of banking and government examinations. They are primarily about determining the number of ways a short group can be created or picked from a larger group of candidates. The simplest way to solve this kind of questions is to apply the formula for permutations and combinations which is NCR = N! / [R! x (N-R)!]

For example, the question in this case or category would be as, “in how many ways can a group of 10 students be selected from a cohort of 200 students?” So, in this case, the answer would be computed using the formula: 200C10 wherein: 200! / [(200-10)! x 10!] would give the answer.

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