21. Suppose \(π_π\) is a non-constant arithmetic sequence such that \(π_1 = 1\). Also, the terms \(π_2 , π_4\) and \(π_9\) form a geometric sequence.
Evaluate \(π_1 + π_2 + π_3 + β― + π_{10}\).
\(π_1 = 1\), misalkan selisihnya adalah \(d\), maka \(π_2 = 1 + d\) \(π_4 = 1 + 3d\) \(π_9 = 1 + 8d\) Karena \(π_2 , π_4\) and \(π_9\) merupakan barisan geometri maka berlaku \(\frac{π_4}{π_2}=\frac{π_9}{π_4}\) \(\frac{1 + 3d}{1 + d}=\frac{1 + 8d}{1 + 3d}\) \(1 + 6d + 9d^2 = 1 + 9d + 8d^2\) \(d^2 = 3d\) Nilai \(d\) yang memenuhi adalah 0 atau 3, karena deret aritmatikanya tidak konstan maka nilai \(d\) yang memenuhi adalah 3. Selanjutnya \(π_1 + π_2 + π_3 + β― + π_{10} = 1 + 4 + 7 + 10 + 13 + 16 + 19 + 22 + 25 + 28 = 145\)
22. Find the least positive integer \(π\) such that \(2^{2021} + π\) is divisible by \(33\).
23. Beatrice has several nuggets. She knew that, when counted in fives, threes and elevens, respectively, \(2, 2\), and \(3\) nuggets remained. What is the least possible number of nuggets she has?
Samakan persamaan (1) dan (3) \(5π + 2 β‘ 3\; πππ\; 11\) \(5(3π) β‘ 1\; πππ\; 11\) \(15π β‘ 1\; πππ\; 11\) \(4π β‘ 1\; πππ\; 11\) Nilai \(k\) terkecil yang memenuhi adalah \(3\) Jadi nilai \(π = 5π + 2 = 5(3π) + 2 = 5(9) + 2 = 45 + 2 = 47\)
24. Find the largest five-digit positive integer whose digits have a product equal to \(7!\)
25. There are \(9\) cards each written with numbers \(1, 2, 2, 3, 3, 3, 4, 5\) and \(6\). Cards with odd numbers are coloured red and the rest are coloured blue. How many ways to arrange all \(9\) cards in a row such that the number on each red card is less than or equal to that on every red card to its right?