Which of the following numbers will replace the question mark (?) in the given series?
7, 17, ?, 137, 407, 1217
Show answer & explanation
Correct answer: D
Explanation
The correct answer is option 4 i.e. 47.
7 × 3 - 4 = 17, 17 × 3 - 4 = 47, 47 × 3 - 4 = 137, 137 × 3 - 4 = 411 - 4 = 407, 407 × 3 - 4 = 1217