Identify the missing number in the following number sequence.
20, 15, 40, 30, 120, 90, ?, 360
Show answer & explanation
Correct answer: D
Explanation
Given Sequence: 20, 15, 40, 30, 120, 90, ?, 360
To find the missing number, look at the sequence as two alternating sub- sequence:
Sub- sequence 1 (Odd position): 20, 40, 120, ?
Sub- sequence 2 (Even position): 15, 30, 90, 360
Analyze Sub- sequence 1:
20×2 = 40
40 × 3 = 120
Following the pattern (multiply by 2, 3,4…), the next step is:
120 × 4 = 480(missing term)
Verify with sub – sequence 2:
15×2 = 30
30× 3 = 90
90×4 = 360
Hence, the correct answer is option (4).