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

3.OA.D9, 3.OA.B5

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.

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

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.

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.

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.

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

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