Tiêu đề Maths XI - Permutations - Permutations when repetitions are allowed.ppt.ppt.pptx.ppt ✅

PERMUTATIONS WHEN REPETITIONS ARE ALLOWED In the previous section, we have learnt the permutations of n distinct things taken r(≤n) at a time when repetition of things is not allowed. Consider 4 distinct things A, B, C, D. We know that we get 4P2 permutations by taking 2 at a time from the above 4 letters, Those are AB, BA, AC, CA, AD, DA, BC, CB, BD, DB, CD and DC. if repetition is not allowed. Observe that in those 12 permutations, each letter occurs only once.
If repetition is allowed, So, the number of permutations, of n distinct things in addition to the above 12 permutations we get 4 more permutations which are AA, BB, CC, DD. taken r at a time is not equal to npr if repetition is allowed. Now, we are going to learn about the number of permutations of n distinct things taken r at a time when repetition of things is allowed.