🔢 Number & Letter Series

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Look at the number series: 4, 6, 10, 18, 34, ? What number should come in place of the question mark?

Answer: 66

💡 Find the difference between each pair of terms. From 4 to 6 the gap is 2. From 6 to 10 the gap is 4. From 10 to 18 the gap is 8. From 18 to 34 the gap is 16. So the gaps are 2, 4, 8, 16, which double each time. The next gap must be 16 x 2 = 32. Add this to the last term: 34 + 32 = 66. So the answer is 66. If you wrongly added 16 again you would get 50 (option A). If you added 24 you would get 58 (option C). If you doubled 34 you would get 68 (option D). Only 66 follows the correct doubling-difference rule.

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