Q.The total amount of an invoice, which already includes GST at 5%, is ₹2,100. Find the taxable value of the goods and the GST charged.

For a tax-inclusive price, divide by $\left(1+\tfrac{g}{100}\right)$ to recover the taxable value.

The $₹2{,}100$ is inclusive of $5\%$ GST, so $\text{invoice}=\text{taxable value}\times1.05$. Recover the taxable value by dividing:

The GST is the difference:

$\text{GST}=2100-2000=₹100.$ …

Taking $5\%$ of the total $₹2{,}100$ (i.e. $₹105$) as the GST. That subtracts tax from a base that already includes it; the correc …