Brain Teasers and Puzzles 

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.

Workings

Hint
What is the difference between each number?

Answer
14.

Add 3 to the previous term.

Workings

Hint
There are two merged sequences.

Answer
10.

Reasoning
There are two sequences mixed together.

0 1 2 3 4 5

and

0 2 4 6 8 {?}

Workings

Hint
Fill the 9-litre container first.

Answer
Here are the contents of the containers after each stage:

A = 9 litres, B = 4 litres
A     B
9     0          fill A
5     4          fill B from A (leaving 5 litres in A)
5     0          empty B
1     4          fill B from A (leaving 1 litre in A)
1     0          empty B
0     1          fill B from A
9     1          fill A
6     4          fill B from A (only 3 more litres fit in B)
6     0          empty B

This leaves 6 litres in container A.