When you multiply by the two decimals count how many places(numbers) are behind each decimal for a number and add for both of them
For Example
3.4-> There is one place (Number) behind the decimal.
x 6.8 -> there is one place(Number) behind the decimal add how many numbers behind the decimal from both numbers 23.12-> since there are 2 Numbers/ places behind the decimal in the numbers multiplied you move the decimal 2 places / Numbers In the product.
