 Using ×4 facts to solve ×8 facts

# Using ×4 facts to solve ×8 facts

I can use what I know about the 4 times table to solve 8 times table facts

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## General

Students use their knowledge of the 4 times table to solve facts from the 8 times table.

3.OA.D9, 3.OA.B5

## Learning Objective

Discuss with students that they can apply facts they already know, about the 4 times table, to solve facts they don't yet know. This saves time because they don't have to start over with every fact.

## Introduction

Students are asked to give the product of the images presented.

## Instruction

Explain to students that they can use their knowledge of 4 times table facts to solve 8 times tables. Do this by having students drag toys to boxes. Show that 2 x 4, doubled, is the same as 2 x 8. Show the same using 5 x 4 to help solve 5 x 8. Have students solve the next problems applying the 4 times table facts to solve the 8 times tables problems. Remind students that if they know the product of a x4 fact, they can double it to solve a x8 fact. Have students discuss and explain their thinking to a partner. Next show a the x4 facts and their accompanying x8 facts to 10 and have students solve for the products. Have the class practice with a game. Spin the wheel to get a number. Multiply it by 4 and then use the answer to solve the related x8 fact. Then practice some word problems with the class that use x4 knowledge to solve a x8 problem.

## Quiz

Students start by giving the product within the 4 times table and then are asked to solve the related 8 times table facts. They are then asked to solve word problems that ask students to use doubling.

## Closing

Discuss with students that they can use their knowledge of 4 times table to solve facts from the 8 times table. Explain that by using this knowledge they don't have to solve from scratch and that they make their calculations easier. Close by playing a game. Students must spin the wheel and multiply the given number by 4 and then use that answer to solve the x8 fact.

## Teaching tips

Students who have difficulty can visualize the doubling process by drawing/writing marks on a sheet of scratch paper.

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