Coding, Series & Patterns› Number & Letter Series
Find out the odd one in the following series : 2, 4, 7, 11.5, 18.25, 28.375, 42.5625
Answer d.
The answer is (d) 42.5625. The gaps between terms grow by a factor of 1.5, so the last term should be 43.5625, not 42.5625. Write the differences between consecutive terms: 4 - 2 = 2; 7 - 4 = 3; 11.5 - 7 = 4.5; 18.25 - 11.5 = 6.75; 28.375 - 18.25 = 10.125. Now compare them: 2 x 1.5 = 3; 3 x 1.5 = 4.5; 4.5 x 1.5 = 6.75; 6.75 x 1.5 = 10.125. So each difference is 1.5 times the one before. The next difference must be 10.125 x 1.5 = 15.1875. The last term should then be 28.375 + 15.1875 = 43.5625. The series gives 42.5625, which is exactly 1 less, so 42.5625 is the odd one. All earlier terms (2, 4, 7, 11.5, 18.25, 28.375) fit the rule.
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