SSC CGL 23 AUGUST 2017 REASONING QUESTION 8 SHIFT 3

8.A series is given, with one term missing. Choose the correct alternative from the given ones that will complete the series.
U, T, R, O, K ?
Options:
1. G
2. H
3. E
4. F
Answer:4
 F K   O  R   T   U
 6  11(15-4), 15(18-3), 18(20-2), 20(21-1), 21
(11-5)