Which of the following numbers will replace the question mark (?) in the given series?
73, 57, 43, 31, ?, 13
Show answer & explanation
Correct answer: D
Explanation
The correct answer is option 4 i.e. 21.
Given series: 73, 57, 43, 31, ?, 13
73 - 16 = 57, 57 - 14 = 43; 43 - 12 = 31, 31 - 10 = 21, 21 - 8 = 13