Match patterns - Number patterns

In Year 4 we've been exploring number patterns using headless matches. First of all we made step 1, step 2 and step 3 of a pattern:

5       10       15

3     6     9

Keeping on going we got to step numbers further on too:

The idea was to work out how the pattern was growing and then, without making it, to say how many matches would be in the 20th step. Quite tricky with some of the patterns!