A series is given with one term missing. Choose the correct alternative from the given ones that will complete the series.
1, 7, 42, 210, 840, ?
- A1240
- B2640
- C1680
- D2520
Solution & Step-by-step Explanation
Let's investigate the multiplication factor between each consecutive term in the series:
1×7=7
7×6=42
42×5=210
210×4=840
The multiplication factor decreases by 1 at each successive step (×7,×6,×5,×4).
Thus, the next factor must be ×3:
840×3=2520
1×7=7
7×6=42
42×5=210
210×4=840
The multiplication factor decreases by 1 at each successive step (×7,×6,×5,×4).
Thus, the next factor must be ×3:
840×3=2520