Miriam says that she uses estimating to figure out where the decimal point goes when she multiplies decimals. For example, given the problem 1.2 x 0.98, she says that a reasonable estimate is 1.2 x 1 = 1.2. In fact, she even thinks that 1 x 1 is a good enough estimate to help her figure out where the decimal point goes. Then, she multiplies 12 x 98 to get 1,176. She says that this lets her know that the actual answer is 1.176.

Does Miriam’s estimation approach work for all decimals?

(Source: Adapted from Bits and Pieces 3 – Connected Mathematics, 2006)