Q.An invoice shows the total amount payable for a product, inclusive of CGST and SGST at 6% each (12% total GST), as Rs 3,360. Find the base price of the product (excluding GST) and the amounts of CGST and SGST separately.

Since the invoice total is tax-inclusive, the combined rate must be reversed first to recover the base price.

Total GST rate = 6% + 6% = 12%, so the invoice total represents 112% of the base price P: 1.12P = 3,360.

Solving, P = 3,360 ÷ 1.12 = Rs 3,000.

CGST = 3,000 × 6/100 = Rs 180; SGST = 3,000 × 6/100 = Rs 180. …

Alternative — unitary method: the invoice total (Rs 3,360) represents 112 parts of the base price, so 1 part = 3,360 ÷ 112 = 30, giving the base price (10 …

As with the Sales Tax reverse example, the most common error is applying 6% directly to the given invoice total (Rs 3,360) instead of first recovering the base price. The base price must always be found FIRST, by divid …