Thus, the total ways to select 7 stocks = 10 × 6 × 3 = 180 ways.
2 utility stocks out of 3 utility stocks can be selected in 3C 2 = 3 ways. 2 transportation stocks out of 4 transportation stocks can be selected in 4C 2 = 6 ways. 3 industrial stocks out of 5 industrial stock can be selected in 5C 3 = 10 ways. Notice the keyword ‘AND’ which indicates all the above 3 events have to occur simultaneously.īy the application of nC r formula, we can write:. He needs to select 2 utility stocks out of 3 utility stocks. He needs to select 2 transportation stocks out of 4 transportation stocks AND,. He needs to select 3 industrial stocks out of 5 industrial stock AND,. The analyst needs to form a different combination of 7 different stocks. Now, we can easily identify that this is selection question, right? Notice the underlined keywords ‘Choose’ and ‘Combinations’ 
If the analyst can choose from 5 industrial stocks, 4 transportation stocks, and 3 utility stocks, how many different combinations of 7 stocks are possible? Q 2 – An analyst will recommend a combination of 3 industrial stocks, 2 transportation stocks, and 2 utility stocks. Now, let us solve a slightly difficult question.
By the application of nC r formula, we can select 3 members from 9 members in 9c 3 ways, which. Thus, we have to select 3 members among 9. Now, in the question, we are asked to select a committee of 4 members from 10 members and John is already a part of the committee. And for selection, we apply the nC r formula to arrive at the answer. Notice the underlined keyword ‘select’ in the question. In how many ways the committee can be formed. As the owner of the society, John is already a member of the committee. Q 1 – In a society of 10 members, we have to select a committee of 4 members. Let us see the application of the above keywords in two GMAT permutation and combination problems. Achieve GMAT 740+ with our AI-driven tools that you personalized feedback at every step of your GMAT journey. Whenever you read a question, look for the above keywords as these are the useful indicators that clearly tells us that the question is a combination question.īegin your GMAT preparation with the only prep company that has delivered more than 700+ scores than any other GMAT club partner. Important keywords to identify a combination question: Now, instead of solving this manually, let us apply the keyword approach to solve this question. Thus, we can have only 3 doubles teams from 3 players. Q – From 3 players, A, B, and C, how many doubles team can be formed?įrom 3 players A, B, and C, the teams of 2-players can be: Let us understand the concept of combination by solving example 1. Keyword approach to identify combination questions This simple example clearly shows that the understanding of permutation and combination can help to decide when arrangement matters and when selection matters. From 3 letters, A, B, and C, how many 2-digit words can be formed?ĭo both the examples look the same to you?. From 3 players, A, B, and C, how many doubles team can be formed?. To clarify this confusion, let us discuss two simple cases: 
In most of the permutation and combination questions, we arrive at a point where we need to select or arrange a few things and many students fall prey to the same mistake of applying selection in place of arrangement and vice-versa.
#WHAT IS A PERMUTATION IN MATH FREE#
One is a verbose description of the mapping: $$\sigma = \begin$ takes $5$ to $2$, as before.Take a free mock A general case on the difference between permutation and combination questions Permutations are represented in two ways.
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