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Category: Permutation and Combination

There-are-4-identical-mathematics-books-2-identical-physics-books-2-identical-chemistry-books-and-2-identical-biology-books-in-how-many-ways-can-you-compile-the-10-books-such-that-same-books-are-n

Question Number 112934 by mr W last updated on 10/Sep/20 $$\mathrm{There}\:\mathrm{are}\:\mathrm{4}\:\mathrm{identical}\:\mathrm{mathematics} \\ $$$$\mathrm{books},\:\mathrm{2}\:\mathrm{identical}\:\mathrm{physics}\:\mathrm{books},\:\mathrm{2} \\ $$$$\mathrm{identical}\:\mathrm{chemistry}\:\mathrm{books}\:\mathrm{and}\:\mathrm{2} \\ $$$$\mathrm{identical}\:\mathrm{biology}\:\mathrm{books}.\:\mathrm{in}\:\mathrm{how}\:\mathrm{many} \\ $$$$\mathrm{ways}\:\:\mathrm{can}\:\mathrm{you}\:\mathrm{compile}\:\mathrm{the}\:\mathrm{10}\:\mathrm{books} \\ $$$$\mathrm{such}\:\mathrm{that}\:\mathrm{same}\:\mathrm{books}\:\mathrm{are}\:\mathrm{not}\:\mathrm{mutually} \\ $$$$\mathrm{adjacent}. \\ $$…

In-a-chess-board-number-of-unit-squares-with-1-one-vertex-common-2-2-vertices-common-3-2-sides-common-

Question Number 178454 by SLVR last updated on 16/Oct/22 $${In}\:{a}\:{chess}\:{board}\:{number}\:{of}\:{unit}\:{squares} \\ $$$$\left.{with}\:\mathrm{1}\right){one}\:{vertex}\:{common}? \\ $$$$\left.\mathrm{2}\right)\mathrm{2}\:{vertices}\:{common}?? \\ $$$$\left.\mathrm{3}\right)\mathrm{2}\:{sides}\:{common}?? \\ $$ Answered by SLVR last updated on 16/Oct/22…

How-many-5-digit-numbers-with-different-digits-are-multiple-of-9-

Question Number 178395 by mr W last updated on 16/Oct/22 $${How}\:{many}\:\mathrm{5}\:{digit}\:{numbers}\:{with} \\ $$$${different}\:{digits}\:{are}\:{multiple}\:{of}\:\mathrm{9}? \\ $$ Answered by cortano1 last updated on 16/Oct/22 $$\left(\mathrm{1}\right)\mathrm{1}+\mathrm{5}+\mathrm{6}+\mathrm{7}+\mathrm{8}\Rightarrow\mathrm{5}! \\ $$$$\left(\mathrm{2}\right)\mathrm{1}+\mathrm{2}+\mathrm{3}+\mathrm{4}+\mathrm{8}\Rightarrow\mathrm{5}!…

There-are-2016-straight-lines-drawn-on-a-board-such-that-1-2-of-the-lines-are-parallel-to-one-another-3-8-of-them-meet-at-a-point-and-each-of-the-remaining-ones-intersect-with-all-other-lines-on-

Question Number 112812 by Aina Samuel Temidayo last updated on 09/Sep/20 $$\mathrm{There}\:\mathrm{are}\:\mathrm{2016}\:\mathrm{straight}\:\mathrm{lines}\:\mathrm{drawn}\:\mathrm{on} \\ $$$$\mathrm{a}\:\mathrm{board}\:\mathrm{such}\:\mathrm{that}\:\frac{\mathrm{1}}{\mathrm{2}}\:\mathrm{of}\:\mathrm{the}\:\mathrm{lines}\:\mathrm{are} \\ $$$$\mathrm{parallel}\:\mathrm{to}\:\mathrm{one}\:\mathrm{another}.\:\frac{\mathrm{3}}{\mathrm{8}}\:\mathrm{of}\:\mathrm{them} \\ $$$$\mathrm{meet}\:\mathrm{at}\:\mathrm{a}\:\mathrm{point}\:\mathrm{and}\:\mathrm{each}\:\mathrm{of}\:\mathrm{the} \\ $$$$\mathrm{remaining}\:\mathrm{ones}\:\mathrm{intersect}\:\mathrm{with}\:\mathrm{all} \\ $$$$\mathrm{other}\:\mathrm{lines}\:\mathrm{on}\:\mathrm{the}\:\mathrm{board}.\:\mathrm{Determine} \\ $$$$\mathrm{the}\:\mathrm{total}\:\mathrm{number}\:\mathrm{of}\:\mathrm{intersections} \\…

What-is-the-maximum-number-of-points-to-be-distributed-within-a-3-6-to-ensure-that-there-are-no-two-points-whose-distance-apart-is-less-than-2-

Question Number 112534 by Aina Samuel Temidayo last updated on 08/Sep/20 $$\mathrm{What}\:\mathrm{is}\:\mathrm{the}\:\mathrm{maximum}\:\mathrm{number} \\ $$$$\mathrm{of}\:\mathrm{points}\:\mathrm{to}\:\mathrm{be}\:\mathrm{distributed}\:\mathrm{within} \\ $$$$\mathrm{a}\:\mathrm{3}×\mathrm{6}\:\mathrm{to}\:\mathrm{ensure}\:\mathrm{that}\:\mathrm{there}\:\mathrm{are}\:\mathrm{no}\:\mathrm{two} \\ $$$$\mathrm{points}\:\mathrm{whose}\:\mathrm{distance}\:\mathrm{apart}\:\mathrm{is}\:\mathrm{less} \\ $$$$\mathrm{than}\:\sqrt{\mathrm{2}}? \\ $$ Commented by Aina…

Find-the-minimum-number-of-n-integers-to-be-selected-from-S-1-2-3-11-so-that-the-difference-of-two-of-the-n-integers-is-7-

Question Number 112533 by Aina Samuel Temidayo last updated on 08/Sep/20 $$\mathrm{Find}\:\mathrm{the}\:\mathrm{minimum}\:\mathrm{number}\:\mathrm{of}\:\mathrm{n} \\ $$$$\mathrm{integers}\:\mathrm{to}\:\mathrm{be}\:\mathrm{selected}\:\mathrm{from} \\ $$$$\mathrm{S}=\left\{\mathrm{1},\mathrm{2},\mathrm{3},…\mathrm{11}\right\}\:\mathrm{so}\:\mathrm{that}\:\mathrm{the}\:\mathrm{difference} \\ $$$$\mathrm{of}\:\mathrm{two}\:\mathrm{of}\:\mathrm{the}\:\mathrm{n}\:\mathrm{integers}\:\mathrm{is}\:\mathrm{7}. \\ $$ Commented by Aina Samuel Temidayo…

A-rectangular-cardboard-is-8cm-long-and-6cm-wide-What-is-the-least-number-of-beads-you-can-arrange-on-the-board-such-that-there-are-at-least-two-of-the-beads-that-are-less-than-10-cm-apart-

Question Number 112531 by Aina Samuel Temidayo last updated on 08/Sep/20 $$\mathrm{A}\:\mathrm{rectangular}\:\mathrm{cardboard}\:\mathrm{is}\:\mathrm{8cm}\:\mathrm{long} \\ $$$$\mathrm{and}\:\mathrm{6cm}\:\mathrm{wide}.\:\mathrm{What}\:\mathrm{is}\:\mathrm{the}\:\mathrm{least} \\ $$$$\mathrm{number}\:\mathrm{of}\:\mathrm{beads}\:\mathrm{you}\:\mathrm{can}\:\mathrm{arrange}\:\mathrm{on} \\ $$$$\mathrm{the}\:\mathrm{board}\:\mathrm{such}\:\mathrm{that}\:\mathrm{there}\:\mathrm{are}\:\mathrm{at}\:\mathrm{least} \\ $$$$\mathrm{two}\:\mathrm{of}\:\mathrm{the}\:\mathrm{beads}\:\mathrm{that}\:\mathrm{are}\:\mathrm{less}\:\mathrm{than} \\ $$$$\sqrt{\mathrm{10}}\mathrm{cm}\:\mathrm{apart}. \\ $$ Commented…

n-1-11-1-n-1-4n-2-4n-n-1-please-help-

Question Number 112195 by 675480065 last updated on 06/Sep/20 $$\underset{\mathrm{n}=\mathrm{1}\:} {\overset{\mathrm{11}} {\sum}}\frac{\left(−\mathrm{1}\right)^{\mathrm{n}+\mathrm{1}} \left(\mathrm{4n}+\mathrm{2}\right)}{\mathrm{4n}\left(\mathrm{n}+\mathrm{1}\right)} \\ $$$$\mathrm{please}\:\mathrm{help} \\ $$ Answered by MJS_new last updated on 06/Sep/20 $$\mathrm{simply}\:\mathrm{calculate}\:\mathrm{it}!\:\mathrm{it}'\mathrm{s}\:\mathrm{only}\:\mathrm{the}\:\mathrm{sum}\:\mathrm{of}\:\mathrm{11}…