The formula for permutation is nPr=(n−r)!n!
8P3=(8−3)!8!
=5!8!
=8×7×6
=336
The formula for combination is nCr=r!(n−r)!n!
10C3=3!×7!10!
=3×2×110×9×8
=6720
=120
Therefore:
8P3−10C3=336−120
=216
(A) matches with (III) 216
8P5=(8−5)!8!
=3!8!
=8×7×6×5×4
=6720
(B) matches with (IV) 6720
nP4=n(n−1)(n−2)(n−3)=360
For n=6:
6×5×4×3=360
(C) matches with (I) 6
nC2=2n(n−1)=210
n(n−1)=420
For n=21:
21×20=420
2420=210
(D) matches with (II) 21
Final Matching:
(A) → (III) 216
(B) → (IV) 6720
(C) → (I) 6
(D) → (II) 21