Addition and Subtraction: Practice and Estimation

Share Solutions. After students have finished solving the problems ask them to share their solutions and their strategies with the class. Possible solutions for two problems are provided.

For Question 4A, students need to find an exact answer. Students can add 6 to 2394 to make it easier to subtract using mental math, 2394 + 6 = 2400. They can then subtract 20 from 5620 to make it a convenient number, 5620 – 20 = 5600. Students can then mentally subtract 5600 – 2400 = 3200. Students then need to add the 20 and the 6 to their answer 3200 + 20 + 6 = 3226. For Question 4B, students can use addition to check their to make sure their answer is correct, 3226 + 2394 = 5620.

Students can use estimation to find the answer for Question 5. Students can round each of the amounts of candy for March and April to the nearest 100. For March 3306 can be rounded to 3300 and the amount of candy for April would be 4900. Students can then add these numbers using expanded form.

Students might also round to the nearest thousand, 3000 + 5000 = 8000 pieces of candy for October.

Ask students to complete Check-In: Questions 7–8 in the Student Guide. Remind them to use the Math Practices previously discussed to guide their written work.

Peer or Self-Assessment. Ask students to review a partner's work or ask students to review their own work using the Student-to-Student Addition and Subtraction: Practice and Estimation Check-In: Questions 7–8 Feedback Box Assessment Master in the Teacher Guide. You can ask students to revise their work using a different color pencil based on their self-assessment or peer review.