# ACC-0001 — GST on a tax invoice (FY2025-26, hypothetical)

## Answers

| Part | Description | Amount |
|------|-------------|--------|
| **(a)** | GST included in the invoice | **$100.00** |
| **(b)** | GST-exclusive price | **$1,000.00** |

## Working

The invoice total of **$1,100** is GST-inclusive at the standard Australian rate of **10%**.

For a GST-inclusive amount, the GST-exclusive base is:

\[
\text{GST-exclusive} = \frac{\text{GST-inclusive}}{1 + 0.10} = \frac{1{,}100}{1.1} = 1{,}000
\]

The GST component is the difference (equivalently, one-eleventh of the inclusive price when the rate is 10%):

\[
\text{GST} = 1{,}100 - 1{,}000 = 100
\]

Check: $1,000 × 10% = $100 GST; $1,000 + $100 = $1,100.

## Approach

Closed-book arithmetic only: treat $1,100 as 110% of the ex-GST price, divide by 1.1 for (b), then subtract for (a). No external sources or inputs beyond the task statement.