Insert the missing number in the following : 3, 8, 18, 23, 33, ?, 48
2009
Insert the missing number in the following :
3, 8, 18, 23, 33, ?, 48
Answer: C. 38 — ConceptIn number-series problems, inspect the successive differences between adjacent terms. A repeating cycle of differences can generate the sequence even…
- A.
37
- B.
40
- C.
38
- D.
45
Attempted by 5 students.
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Correct answer: C
Concept
In number-series problems, inspect the successive differences between adjacent terms. A repeating cycle of differences can generate the sequence even when the terms do not have one constant gap.
Application
From 3 to 8, the difference is +5.
From 8 to 18, the difference is +10.
From 18 to 23, the difference is +5.
From 23 to 33, the difference is +10.
The differences therefore repeat as +5, +10. The next term is 33 + 5 = 38.
Applying the next difference gives 38 + 10 = 48, which matches the final term.
Cross-check
The odd-position terms 3, 18, 33, 48 each increase by 15, while the even-position terms 8, 23, 38 also each increase by 15. Both views give the missing number 38.