Hi,
I'm not familiar with the Sloman book
Economics. However, having at a quick look on Amazon it does appear to cover similar ground. So, you may well be able to "get away" with using it instead of
Economics for Business. However, the topics covered in the two books are unlikely to be exactly the same and as Economics for Business is the Core Reading for CT7, using a different book means you won't actually have the Core Reading.
One approach could be to start working through the Course Notes and see how you get on. If you find that there are topics you don't fully understand and that aren't explained further in your textbook, then maybe you should then consider getting Economics for Business.
Finally, if you contact the Institute and Faculty's library in Oxford (
http://www.actuaries.org.uk/research-and-resources/pages/library-services), then they will probably have a copy of Economics for Business that you could borrow to compare the books and decide whether or not you want to purchase it.
In general, although you could probably manage without the recommended textbook, I'd probably encourage you to get a copy just to be on the safe side.
I hope this helps.
Graham
