Gemini 3.1 Pro Preview vs GPT-5.5 for bookkeeping

**1. Work out the difference**
The bank statement closing balance is £8,412.55. 
The cash book closing balance is £8,376.55. 
The difference is **£36.00** (£8,412.55 - £8,376.55). 
*(Note: The outstanding unpresented cheque and uncredited lodgement of £120.00 perfectly cancel each other out, so they do not affect this £36.00 difference).*

**2. What kind of error is it?**
This is a **transposition error** (specifically, reversing two adjacent digits when recording a number). 

**3. The arithmetic rule that identifies this class of error at a gl…

Adjusted bank statement balance:

- Bank statement closing balance: **£8,412.55**
- Less unpresented cheque: **£120.00**
- Add lodgement not yet credited: **£120.00**

These cancel, so adjusted bank balance remains **£8,412.55**.

Cash book balance: **£8,376.55**

So the difference is:

**£8,412.55 − £8,376.55 = £36.00**

The bank is **£36.00 higher** than the cash book.

This is the classic sign of a **transposition error**: **£451** and **£415** have been interchanged.

Arithmetic rule: a transposition error is usually divisible by **9**. Her…