Category Archives: Combinatorics

MATHCOUNTS Exercises – 5

Posted on December 26, 2019 by kevin

MATHCOUNTS 2016-2017 – 155 Twelve couples participate in a fitness retreat. One strength-building exercise requires participants to form teams of three so that the two people who make up a couple are not on the same team. How many different … Continue reading →

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Problem of the Day – November 27, 2019

Posted on November 27, 2019 by kevin

How many 4-digit numbers are there without digit 2 and 3, such as 7450? How many of them are there with at least one digits as 2 or 3, such as 1200, 3401, 1234?

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Problem of the Day – November 26, 2019

Posted on November 26, 2019 by kevin

How many 4-digit numbers are there with digits in absolute descending order, such as 8520? And how many 4-digit numbers are there with digits in absolute ascending order, such as 3569?

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