Question:
Find the number of permutations of n distinct things taken r together, in which 3 particular things must occur together.
Solution:
Permutations of n distinct things taken r together =nCr
And when 3 particular things must occur together, we get,
= n – 3Cr – 3
= n – 3Cr – 3 × (r – 2)! × 3!
Click here to get exam-ready with eSaral
For making your preparation journey smoother of JEE, NEET and Class 8 to 10, grab our app now.