PS/IS 686 | Brooklyn, NY

Fifth Grade Math: Big Ideas in Multiplying and Dividing Decimals

Fifth graders are just wrapping up their decimal unit and will have a test on Monday.  As we explored decimal multiplication and division, a number of big ideas emerged, such as what happens to the quotient when the divisor is less than one? What happens to the product when one of the factors is less than one?  It was fun to see their reactions when they realized that the product can get smaller when we multiply, and the quotient can get larger when we divide.  We will revisit this idea again as we begin our fraction unit.

We also used our understandings of whole number division to help us with decimal division.  In 4th grade, students learned  that when we multiply both the dividend and divisor by the same number, we create an equivalent expression.  This is a big help when working with decimals.  We can use this understanding to create an easier problem.  If we have 5.42 divided by 0.35, we can multiply both the dividend and divisor by 100 to get 542 divided by 35, which will have the same quotient as the original problem.  This is the reason we can use the trick of moving the decimal point.

Enjoy the rest of you week!