Medium Puzzles 

Workings

Hint
A very common sequence, but in base 8!

Answer
13.

Odd numbers expressed in base 8, 11 in base 8 = 13.

Workings

Hint
Look at the gaps in the alphabetic position.

Answer
V.

Skip three and two letters alternately.

Workings

Hint
The answers are related to time.

Answer
60.

The numbers represent 100 years in a century, 365 days in a year, 24 hours in a day, 60 minutes in an hour, and 60 seconds in a minute.

Workings

Hint
Try writing the numbers as words.

Answer
22.

This is a sequence of numbers that contain the letter O.

One, two, four, fourteen, twenty-one, twenty-two.