Thanks very much. On page 31, I added a DR dated 31/1/13 for 5000 under the Supplier Account, and added a rent account with a DR dated 31/3/13 for 100. Now the trial balance makes sense!
Lesson learnt for me is to check the dates of transaction to make sure every transaction has a double entry.
Is that meant to be a test or is this an ommission in the text?