Bigger Products

The same method handles bigger decimals. In 3.5 × 1.2, multiply 35 · 12 as whole numbers. Work it in parts: 35 · 10 is 350 and 35 · 2 is 70, so 35 · 12 is 420.

Now count places: one in 3.5 and one in 1.2, so two in the answer. 420 with two places is 4.20, and the zero at the end can go: 4.2.

Always check with an estimate. 3.5 is between 3 and 4, and 1.2 is a little more than 1, so the product should be a little more than 3.5. 4.2 fits; 42 or 0.42 would not, and a check like this tells you at once that the point landed in the wrong place.