Solved IB ACIO Question
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Q · Missing Numbermedium · 45s
Identify the missing number in the series: 1, 3, 6, 10, ?, 21
TopicMissing Number
Question Typemultiple choice
Difficultymedium
Marking+1 / −0.25
Test Duration30 min
Step-by-Step Solution
The complete worked solution.
Every step explained — no skipped algebra.
The sequence is triangle numbers. The 5th term is 15.
Final Answer: Option A — 15