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# Permutation & Combination

When learning the concept of permutation and combination in JC H2 Math Classes, you will come across some interesting concepts like the number of arrangement of objects in a line. In addition, you will learn how to calculate the number of arrangement of objects in circle. These concept will also take into account of cases like repetition and restriction.

## Permutation Formula

n!/(n-r)!
This formula calculates the number of permutations of n things taken r at a time

## Combination Formula

n!/[(n-r)!r!]
This formula calculates the number of combinations of n things taken r at a time

## Number of permutations of n things when there are n1, n2, …, nk repeated items.

n!/(n1!n2!…nk!)

Question

There are few letters, namely “GIIILK”.

1. How many different ways the words can be arranged in a row?
2. How many ways of arrangement that all three letters of “I” are together?

1. 20
2. 6

## About the Singapore Math Tutor - Dr Loo

I am a PhD holder with 9 years of teaching experience on teaching quantitative subjects at secondary school and university levels. My expertise are mathematics, statistics, econometrics, finance and machine learning.

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Among the Singapore math tuition that I provide, this includes Singapore secondary math tuition (E-math tuition & A-math tuition) and also JC Math Tuition (H1 Math Tuition & H2 Math Tuition). On the other hand, my statistics tuition in Singapore mostly focus on pre-university level until postgraduate level. For those who are looking for online tutoring service, the online O-level math tuition and online A-level math tuition are also available.

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