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In how many of the distinct permutations of the letters in MISSISSIPPI do the four I’s not come together?

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Question

In how many of the distinct permutations of the letters in MISSISSIPPI do the four I’s not come together?

Sum
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Solution

In the given word MISSISSIPPI, I appears 4 times, S appears 4 times, P appears 2 times, and M appears just once.

Therefore, number of distinct permutations of the letters in the given word

= `(11!)/(4!4!2!)`

= `(11 xx 10 xx 9 xx 8 xx 7 xx 6 xx 5 xx 4!)/(4! xx 4 xx 3 xx 2 xx 1 xx 2 xx 1)`

= `(11 xx 10 xx 9 xx 8 xx 7 xx 6 xx 5)/(4 xx 3 xx 2 xx 1xx 2 xx 1)`

= 34650 

There are 4 Is in the given word. When they occur together, they are treated as a single object  for the time being. This single object, together with the remaining 7 objects, will account for 8 objects.

These 8 objects, in which there are 4 Ss and 2 Ps, can be arranged in `(8!)/(4!2!)` ways, i.e., 

840 ways.

Number of arrangements where all Is occur together = 840

Thus, number of distinct permutations of the letters in MISSISSIPPI in which four Is do not come together = 34650 – 840 = 33810

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Chapter 6: Permutations and Combinations - EXERCISE 6.3 [Page 114]

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NCERT Mathematics [English] Class 11
Chapter 6 Permutations and Combinations
EXERCISE 6.3 | Q 10. | Page 114

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