Category: Permutation and Combination

Question Number 154268 by liberty last updated on 16/Sep/21 Commented by mr W last updated on 16/Sep/21 $$8!=40320$$ Commented by liberty last updated…

Question Number 153714 by pete last updated on 09/Sep/21 $$\mathrm{How}\mathrm{many}\mathrm{three}-\mathrm{digit}\mathrm{numbers}\mathrm{can}\mathrm{be}$$$$\mathrm{formed}\mathrm{using}\mathrm{the}\mathrm{digits}2,3,5,7,8\mathrm{if}$$$$\mathrm{the}\mathrm{number}\mathrm{is}\mathrm{odd}\mathrm{and}\mathrm{no}\mathrm{digit}\mathrm{is}\mathrm{repeted}?$$ Answered by EDWIN88 last updated on 09/Sep/21 $$=\:{P}_{\mathrm{1}} ^{\:\mathrm{3}}…

Question Number 22435 by Tinkutara last updated on 18/Oct/17 $$C_0{}^{2n}{C}_n-C_1{}^{2n-2}{C}_n+C_2{}^{2n-4}{C}_n\dots .$$$$\mathrm{equals}\mathrm{to}$$ Terms of…

Question Number 87790 by mathocean1 last updated on 06/Apr/20 $$\mathrm{How}\mathrm{many}\mathrm{handshakes}\mathrm{are}\mathrm{exchanged}$$$$\mathrm{betwen}27\mathrm{boys}?$$ Answered by TANMAY PANACEA. last updated on 06/Apr/20 $$27C_2$$$$=\frac{\mathrm{27}!}{\mathrm{2}!\mathrm{25}!}=\frac{\mathrm{27}×\mathrm{26}}{\mathrm{2}}=\mathrm{351}…

Question Number 87732 by mathocean1 last updated on 05/Apr/20 $$\mathrm{Solve}\mathrm{it}\mathrm{in}\mathbb{N}$$$${\mathrm{C}}_{\mathrm{n}}^3-{\mathrm{C}}_{\mathrm{n}}^2=5+\frac{{\mathrm{n}}^3-{6\mathrm{n}}^2}{6}$$ Commented by Tony Lin last…