[strls]

The books are called "Essential Mathematics" 1 and 2. They correspond to these modules. http://www.openuniversity.edu/courses/modules/mst124 http://www.openuniversity.edu/courses/modules/mst125

Second-hand OU books are usually bought from https://www.universitybooksearch.co.uk/

[learner1215]

Could you provide the direct links for the books used in: MST123, MST124, MST125? I could not find them in your links.

[blacksmith_tb]

If you're not in the UK, I see that Thriftbooks appears to get at least some copies[1].

1: https://www.thriftbooks.com/browse/?b.search=MST124#b.s=most...

[injb]

Search for "Open University MST124" or similar on www.ebay.co.uk or www.amazon.co.uk. There seem to be plenty of copies of 124 available on both at the time of writing.