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Category: Permutation and Combination

1-1-x-n-n-0-n-1-x-n-2-x-2-n-3-x-3-

Question Number 139286 by qaz last updated on 25/Apr/21 $$\frac{\mathrm{1}}{\left(\mathrm{1}−{x}\right)^{{n}} }=\left(\begin{pmatrix}{{n}}\\{\mathrm{0}}\end{pmatrix}\right)+\left(\begin{pmatrix}{{n}}\\{\mathrm{1}}\end{pmatrix}\right){x}+\left(\begin{pmatrix}{{n}}\\{\mathrm{2}}\end{pmatrix}\right){x}^{\mathrm{2}} +\left(\begin{pmatrix}{{n}}\\{\mathrm{3}}\end{pmatrix}\right){x}^{\mathrm{3}} +… \\ $$ Commented by mr W last updated on 25/Apr/21 $${wrong}! \\…

find-the-coefficient-a-k-of-term-x-k-in-r-1-n-1-x-r-with-0-k-n-n-1-2-example-n-100-k-50-

Question Number 73224 by mr W last updated on 09/Nov/19 $${find}\:{the}\:{coefficient}\:{a}_{{k}} \:{of}\:{term}\:{x}^{{k}} \:{in} \\ $$$$\underset{{r}=\mathrm{1}} {\overset{{n}} {\prod}}\left(\mathrm{1}+{x}^{{r}} \right)\:{with}\:\mathrm{0}\leqslant{k}\leqslant\frac{{n}\left({n}+\mathrm{1}\right)}{\mathrm{2}} \\ $$$$ \\ $$$${example}:\:{n}=\mathrm{100},\:{k}=\mathrm{50} \\ $$ Answered…

A-committee-of-3-members-is-to-be-formed-from-8-members-Find-the-number-of-committees-that-can-be-formed-if-two-particular-club-members-cannot-both-be-in-a-committee-

Question Number 138748 by physicstutes last updated on 17/Apr/21 $$\mathrm{A}\:\mathrm{committee}\:\mathrm{of}\:\mathrm{3}\:\mathrm{members}\:\mathrm{is}\:\mathrm{to}\:\mathrm{be}\:\mathrm{formed}\:\mathrm{from}\:\mathrm{8}\:\mathrm{members}. \\ $$$$\mathrm{Find}\:\mathrm{the}\:\mathrm{number}\:\mathrm{of}\:\mathrm{committees}\:\mathrm{that}\:\mathrm{can}\:\mathrm{be}\:\mathrm{formed}\:\mathrm{if}\:\mathrm{two}\:\mathrm{particular} \\ $$$$\mathrm{club}\:\mathrm{members}\:\mathrm{cannot}\:\mathrm{both}\:\mathrm{be}\:\mathrm{in}\:\mathrm{a}\:\mathrm{committee} \\ $$ Answered by mr W last updated on 17/Apr/21 $${C}_{\mathrm{3}}…

Determine-the-term-independent-of-x-in-the-expansion-x-1-x-2-3-x-1-3-1-x-1-x-x-1-2-10-

Question Number 137943 by john_santu last updated on 08/Apr/21 $${Determine}\:{the}\:{term}\:{independent} \\ $$$${of}\:{x}\:{in}\:{the}\:{expansion}\: \\ $$$$\:\:\:\:\left(\frac{{x}+\mathrm{1}}{{x}^{\mathrm{2}/\mathrm{3}} −{x}^{\mathrm{1}/\mathrm{3}} +\mathrm{1}}\:−\frac{{x}−\mathrm{1}}{{x}−{x}^{\mathrm{1}/\mathrm{2}} }\:\right)^{\mathrm{10}} \:. \\ $$ Answered by EDWIN88 last updated…

Evaluate-10-12-14-16-18-20-into-factorial-form-

Question Number 5989 by sanusihammed last updated on 08/Jun/16 $${Evaluate}\:\:\:\mathrm{10}\:×\mathrm{12}\:×\:\mathrm{14}\:×\:\mathrm{16}\:×\:\mathrm{18}\:×\:\mathrm{20}\:\:{into}\:{factorial}\:{form} \\ $$ Answered by prakash jain last updated on 08/Jun/16 $$\mathrm{10}×\mathrm{12}×\mathrm{14}×\mathrm{16}×\mathrm{18}×\mathrm{20} \\ $$$$=\mathrm{2}\left(\mathrm{5}×\mathrm{6}×\mathrm{7}×\mathrm{8}×\mathrm{9}×\mathrm{10}\right)=\frac{\mathrm{2}!\mathrm{10}!}{\mathrm{4}!} \\ $$…