Discussion
Select the number from the given options that can replace the question mark (?) in the following series.
90, 120, 156, 198, 246, ?
Answer: B
The differences between the terms are 120 - 90 = 30, 156 - 120 = 36, 198 - 156 = 42 and 246 - 198 = 48. These differences themselves increase by 6 each time, so the next difference is 54, and the next term is 246 + 54 = 300. The answer is 300, option (B). The option 350 would need a difference of 104, and 296 and 306 do not follow the rise of 6 in the differences, which are 6, 6 and 6 for the earlier terms. Series in which the difference between the terms goes up by a fixed amount are called second-order series, and the same working is used in many number series questions.
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