What should come in place of the question mark (?) in the following number series.
3 7 13 ? 31 43
(a) 18 (b) 19 (c) 23 (d) 21 (e) of these
(d) The given number series is based on the following pattern: 7 + 6 = 13 13 + 8 = 21 21 + 10 = 31 31 + 12 = 43 Hence, the number 21 will replace the question mark.
