Using prime factorisation method:(i) 12, 15 and 21Factor of \\\\(12 = 2 \ imes 2 \ imes 3\\\\)Factor of \\\\(15 = 3 \ imes 5\\\\)Factor of \\\\(21 = 3 \ imes 7\\\\)HCF \\\\((12, 15, 21) = 3\\\\)LCM \\\\((12, 15, 21) = 2 \ imes 2 \ imes 3 \ imes 5 \ imes 7 = 420\\\\)(ii) 17, 23 and 29Factor of \\\\(17 = 1 \ imes 17\\\\)Factor of \\\\(23 = 1 \ imes 23\\\\)Factor of \\\\(29 = 1 \ imes 29\\\\)HCF \\\\((17, 23, 29) = 1\\\\)LCM \\\\((17, 23, 29) = 1 \ imes 17 \ imes 23 \ imes 29 = 11,339\\\\)(iii) 8, 9 and 25Factor of \\\\(8 = 2 \ imes 2 \ imes 2 \ imes 1\\\\)Factor of \\\\(9 = 3 \ imes 3 \ imes 1\\\\)Factor of \\\\(25 = 5 \ imes 5 \ imes 1\\\\)HCF \\\\((8, 9, 25) = 1\\\\)LCM \\\\((8, 9, 25) = 2 \ imes 2 \ imes 2 \ imes 3 \ imes 3 \ imes 5 \ imes 5 = 1,800\\\\)