Can the rule for multiplying decimals be explained to children?
To multiply decimal numbers, you get the number of decimal places in the answer by adding the number of decimal places in the two numbers being multiplied. For example to multiply 3.1 (one decimal place) by 4.02 (two decimal places), first multiply 31 by 402 and put the decimal point in so that there are three (1 & 2) decimal places in the answer. Can this be explained to children? Answer: The algorithm described here is often used in schools to carry out pen and paper calculations of decimal long multiplication. Following the rule does not “justify” or “prove” why it works. A full justification of the rule is given in Foundations for Teaching Arithmetic (Marston and Stacey, 2001). It is important to develop the meaning of decimals by numbers less than one. Area models are a useful way of showing how decimals can be combined through multiplication, while estimation helps children to decide the correct order of magnitude of a result. For example, 0.5 x 0.8 cannot equal 4 or 40 because b
