Q&A for How to Multiply Using the Line Method

A number line is not useful in multiplication. Instead, think of multiplying by 20 as first multiplying by 2 (a relatively easy process) and then multiplying by 10 (which is done easily by moving the decimal point one place to the right). For example, to multiply 45 by 20, first multiply 45 by 2, which is 90. Then multiply 90 by 10: move the decimal point one place to the right, making 900.

Anything multiplied by 0 is 0, so if there is a 0 in the problem, the answer is 0.

Don’t draw the line, but you can put something there as a placeholder. Or, draw the line in a different color but don’t count the intersecting spots because 0 times a number always equals 0.

If you are using decimals, remove the decimal point and when you’re done, count how many digits are after the decimal point for both factors in total. That is how many digits that will be after the decimal point in the product. Place the point back in. If you’re doing a fraction then change it to a decimal first. If it is impossible to change it into a decimal that will work for this method (i.e., the exact value of 1/3 times a number), then you cannot use this method.