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Category: Permutation and Combination

There-are-many-ways-to-arrange-3-red-balls-and-9-black-balls-in-a-circle-so-that-there-are-a-minimum-of-2-black-balls-between-2-adjacent-red-balls-a-180-8-b-240-7-c-364-6-d-282-4

Question Number 200051 by cortano12 last updated on 13/Nov/23 $$ \\ $$$$\mathrm{There}\:\mathrm{are}\:\mathrm{many}\:\mathrm{ways}\:\mathrm{to}\:\mathrm{arrange}\:\mathrm{3}\:\mathrm{red} \\ $$$$\:\mathrm{balls}\:\mathrm{and}\:\mathrm{9}\:\mathrm{black}\:\mathrm{balls}\:\mathrm{in}\:\mathrm{a}\:\mathrm{circle}\: \\ $$$$\mathrm{so}\:\mathrm{that}\:\mathrm{there}\:\mathrm{are}\:\mathrm{a}\:\mathrm{minimum}\:\mathrm{of}\:\mathrm{2} \\ $$$$\mathrm{black}\:\mathrm{balls}\:\mathrm{between}\:\mathrm{2}\:\mathrm{adjacent}\:\mathrm{red} \\ $$$$\mathrm{balls}. \\ $$$$\left(\mathrm{a}\right)\:\mathrm{180}×\mathrm{8}!\:\:\:\:\left(\mathrm{b}\right)\:\mathrm{240}×\mathrm{7}!\:\:\:\:\left(\mathrm{c}\right)\:\mathrm{364}×\mathrm{6}! \\ $$$$\:\left(\mathrm{d}\right)\:\mathrm{282}×\mathrm{4}!\:\:\:\:\left(\mathrm{e}\right)\:\mathrm{144}×\mathrm{5}!\: \\…

What-is-the-probability-that-in-a-class-of-18-people-there-exists-exactly-a-group-of-exactly-3-people-born-on-the-same-day-of-the-week-

Question Number 199353 by mr W last updated on 01/Nov/23 $${What}\:{is}\:{the}\:{probability}\:{that}\:{in}\:{a}\:{class}\: \\ $$$${of}\:\mathrm{18}\:{people},\:{there}\:{exists}\:{exactly}\:{a}\: \\ $$$${group}\:{of}\:{exactly}\:\mathrm{3}\:{people}\:{born}\:{on}\:{the} \\ $$$${same}\:{day}\:{of}\:{the}\:{week}? \\ $$ Commented by AST last updated on…

Find-the-number-of-integers-greater-than-6200-that-can-be-formed-from-the-digits-1-3-6-8-and-9-where-each-digit-is-used-at-most-once-

Question Number 199333 by necx122 last updated on 01/Nov/23 $${Find}\:{the}\:{number}\:{of}\:{integers}\:{greater} \\ $$$${than}\:\mathrm{6200}\:{that}\:{can}\:{be}\:{formed}\:{from} \\ $$$${the}\:{digits}\:\mathrm{1},\mathrm{3},\mathrm{6},\mathrm{8}\:{and}\:\mathrm{9},\:{where}\:{each} \\ $$$${digit}\:{is}\:{used}\:{at}\:{most}\:{once}. \\ $$ Answered by aleks041103 last updated on 01/Nov/23…