Ray's New Primary Arithmetic by Joseph Ray Ray's New Primary Arithmetic by Joseph Ray    

Lesson 69: Multiply by 10

Directions

Have children complete the steps below.

Have children practice until they perfectly master each task.

Steps

STEP 1

Demonstrate multiplication with various physical objects, marks on the board, and/or an abacus with counters (beads).

To teach 2x10 and 10x2, demonstrate with 20 objects of various types and ask:

• How many are 2 groups of 10 coins? (Divide the 20 coins into 2 equal groups of 9.)
• How many are 10 groups of 2 coins? (Divide the 20 coins into 10 equal groups of 2.)
• When children readily call out the correct answers, give them each 20 coins and direct them do the divisions themselves.

Represent the operations using dots or other symbols on the board. Draw the dots and ask:

• How many are 2 groups of 10 dots? (Make 2 groups of 10 dots. Circle each group of 10 dots.)
• How many are 10 groups of 2 dots? (Make 10 groups of 2 dots. Circle each group of 2 dots.)
• When children readily call out the correct answers, direct them to make the marks on the board and circle the groups themselves.

If using an abacus, demonstrate by sliding the counters to illustrate:

• How many are 2 groups of 10 counters? (Slide over 10 counters on 2 rows.)
• How many are 10 groups of 2 counters? (Slide over 2 counters on 10 rows.)
• When children readily call out the correct answers, direct them to slide the counters to make the groups themselves.

STEP 2

Children multiply objects they can't see, but can imagine (bears, mountains, trees).

Ask the following:

• How many are 2 groups of 10 aliens?
• How many are 10 groups of 2 dump trucks?

STEP 3

In this phase, do not mention objects. Children multiply numbers directly.

Ask the following:

• How many are 2 groups of 10?
• How many are 10 groups of 2?
• How many are 2 times 10?
• How many are 10 times 2?

STEP 4

Write the problems listed in the table below on the board. Show the children the symbol for times (x).

Direct children to write and then recite each of these equations as follows:

• 2 times 10 is 20
• 2 x 10 = 20
• 10 times 2 is 20
• 10 x 2 = 20

STEP 5

Repeat steps 1-4 for each combination in the table below until the children master the tasks.

STEP 6

Assess mastery by reading aloud the listed word problems and having the children mentally compute and recite the solutions.

If children have difficulties, repeat the prior phases as needed and then reassess.