Which of the following numbers will complete the given series ?
87, ___, 53, 39, 27.
69
In a number series the terms follow a fixed rule, and the most common rule is a pattern in the differences between consecutive terms. When the known terms are decreasing, find the differences between the terms that are given, see how those differences themselves change, and then extend the pattern backwards to fill the missing place.
Known differences:
\(53 - 39 = 14\)
\(39 - 27 = 12\)
The differences fall by 2 each time, so going backwards they rise by 2.
Missing term = \(53 + 16 = 69\)
Check: \(87 - 69 = 18\)
Differences = 18, 16, 14, 12
If 79 were placed in the gap, the differences would be 8 and 26, which follow no rule. With 77 the differences would be 10 and 24, and with 75 they would be 12 and 22; neither of these continues the steady fall of 2 seen in 14 and 12. Only 69 gives the uniform sequence of differences 18, 16, 14, 12.
Hence, 69.
Important Questions from Number Series
What will come in place of question mark (?) in the following number series?
2, 5, 11, 23, 44, 77, ?
What will come in place of question mark (?) in the following number series?
31, 32, 36, ?, 61, 86
What will come in the place of question mark (?) in the following number series?
3, 6, 18, ?, 630, 6930
What should come in place of the question mark ‘?’ in the following number series?
60, 40, 50, ?, 180, 460
A series is given with one term wrong. Select that wrong term from the given alternatives.
J12, M24, P48, S96, U192
