**Working**

A GST-inclusive price equals the GST-exclusive price × 1.10 (since GST is 10%). Therefore:

- GST-exclusive price = $1,100 ÷ 1.1 = $1,000
- GST amount = $1,100 ÷ 11 = $100 (equivalently, 10% × $1,000 = $100)

**Answers**

| Item | Amount |
|---|---|
| (a) GST included in the invoice | **$100** |
| (b) GST-exclusive price | **$1,000** |

Check: $1,000 + $100 = $1,100 ✓