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

Lesson 94: Divide Where 10 is an Operand or a Result

Directions

Have children complete the steps below.

Have children practice until they perfectly master each task.

Steps

STEP 1

To teach 20 ÷ 2 and 20 ÷ 10, demonstrate with 20 objects of various types.

• Write 10 + 10 = 20 on the board.
• Ask children how times does 10 go into 20? (Divide the 20 objects into 2 groups of 10.)
• Write 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 = 20 on the board.
• Ask children how times does 2 go into 20? (Divide the 20 objects into 10 groups of 2.)
• When children readily call out the correct answers, give them each 20 objects 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 groups of 10 can we form? (Make 2 groups of 10 dots. Circle each group of dots.)
• How many groups of 2 can we form? (Make 10 groups of 2 dots. Circle each group of 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 groups of 10 can we form out of 20 counters? (Slide over 10 counters on 2 rows.)
• How many groups of 2 can we form out of 20 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 divide objects they can't see, but can imagine (bears, mountains, trees).

Ask the following:

• How many times 10 in 20 penguins?
• How many times 2 in 20 icebergs?

STEP 3

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

Ask the following:

• How many times 10 in 20?
• How many times 2 in 20?
• How many are 20 divided by 10?
• How many are 20 divided by 2?

STEP 4

Write the problems listed in the table below on the board. Show the children the symbol for division ('/' or '÷').

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

• 20 divided by 2 is 10
• 20 ÷ 2 = 10
• 20 divided by 10 is 2
• 20 ÷ 10 = 2

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.