Multiplication at the Zoo
Est. Class Sessions: 2Summarizing the Lesson
Questions 11–13 in the Student Guide ask students to solve multiplication problems using appropriate methods based on the numbers in the problems. Have students work with partners to solve the problems in Question 11 and discuss whether it is more efficient to use mental math or paper and pencil. Do not ask students to write their explanations for the problems they solve using mental math, but to be prepared to explain what was “in their head.” Question 12 asks them to choose a problem and explain their thinking. Ask students to share their strategies orally and have the remaining students ask questions for clarification. Question 13 asks students to solve a problem using doubling. This method is often a favorite method of students. As students explain their strategies, make a chart as shown in Figure 9. List the problems students solve with each method under each heading.
Some problems will fall on both sides of the chart.
Ask students how they made their choices:
Possible responses include:
“I look for numbers that are easy to break apart into tens and ones and multiply each part in my head like 21 × 6.”
“I look for 5s multiplied times an even number like 44 × 5. Then I can cut 44 in half and multiply by 10.”
“I look for numbers where I can think about money like 27 × 3. Then I think of quarters and break the 27 into 25 and 2.”
“I look for nines in the ones place like 39 × 4. Then I can multiply by a [multiple of] 10 and then subtract. 40 × 4 = 160 then subtract 4 and get 156.”
Ask students to complete Check-In: Questions 14–15 to assess their progress multiplying 1-digit by 2-digit numbers.
Students can complete the What Were They Thinking? pages in the Student Activity Book for more practice in class or for homework. These pages provide practice using specific mental math strategies and paper-and-pencil procedures. Then students solve a set of problems and choose their own methods.
