Find the pattern: 5, 6, 7 is skipped, 8, 9, 10 is skipped, 11, 12, 13 is skipped, 14, 15, 16 is skipped, 17, 18, so 19 would be skipped. The answer would be 20 and 21.
As for the next problem, it's best if you work backwards and repeat the same method.
The answer would be 2 and 3.
