Question
Find the fourth proportion of (2k - 4), (4k - 8) and
(6k - 12). (Note: 'k' is the largest single-digit composite number.)Solution
'k' = 9 2k - 4 = 2 × 9 - 4 = 14 4k - 8 = 4 × 9 - 8 = 28 6k - 12 = 6 × 9 - 12 = 42 Let the fourth proportion be 'm'. 14 : 28 :: 42 : m So, 14 × m = 28 × 42 Or, 'm' = 84
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