we know that 9*9 = 81, so let's start there.
0.9 * 0.9
one amount has 1 decimal, the second amount has another decimal, so in the product, we must have two decimals, let's do the multiplication without the dot.
09 * 09 = 81
but we must have two decimals, so that becomes 0.81.
0.09 * 0.9
here we do the same, the multiplication without the dot, and then we add as many decimals, in this case is 3 decimals, first term has 2 and the second term has 1 decimal, so the product must have 3 decimals.
009 * 09 = 81
getting those 3 decimals.......... 0.081.
0.009 * 0.9
here we do the same
0009 * 09 = 81
the product needs 4 decimals, so................ 0.0081.
0.009 * 0.09
we do the same here
0009 * 009 = 81
since the product needs 5 decimals................. 0.00081.
