This Math Talk focuses on the relationship between division by 100 and multiplication by 1001. It encourages students to rely on what they know about place value, fractions, decimals, and the relationship between multiplication and division to mentally solve problems. The reasoning elicited here will be helpful when students work with percentages later in the lesson.
Tell students to close their books or devices (or to keep them closed). Reveal one problem at a time. For each problem:
Keep all previous problems and work displayed throughout the talk.
Find the value of each expression mentally.
To involve more students in the conversation, consider asking:
Highlight two points: that dividing a number by 100 gives the same result as multiplying the number by 1001, and that a fraction can be interpreted as division (100105 can be understood as 105÷100).