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

Lesson 46: Subtract Numbers From Up to 18

Directions

Teach children to subtract numbers from up to 18.

Have children practice until they perfectly master the task.

Steps

STEP 1

• Children separate a larger group of up to 18 objects into two smaller groups.
• Repeatedly separate a group of objects into smaller groups per the table below. For example, 9 pencils from 9 pencils leaves 0 pencils, 8 coins from 17 coins leaves 9 coins, and 9 cars from 17 cars leaves 8 cars, etc.

• When children are ready, have them separate the object groups themselves.
• Children must perfectly master the operations listed in the table before proceeding to the next phase of the lesson.

STEP 2

• Children separate groups of objects they can't see, but can imagine (bears, mountains, trees).
• Using the table above as a guide, ask children to call out the answer to questions such as, 'How many are one shoe from ten shoes?' and 'How many are nine frogs from eleven frogs?'
• Give numerous exercises on each number, with constant reviews, until children can recite each operation in the table with great accuracy and rapidity.

STEP 3

• In this phase, do not mention objects. Children subtract numbers directly.
• Using the table above as a guide, ask children to call out the answer to questions such as, 'How many are one from ten?' and 'How many are four from thirteen?'
• Give numerous exercises on each number, with constant reviews, until children can perform each operation with great accuracy and rapidity.

STEP 4

• Direct children to practice writing and reciting the subtraction problems listed in the table above. For example, they would write and then recite:
• 9 from 18 leaves 9
• 18 minus 9 is 9
• 18 - 9 = 9
• Repeat for each combination in the table until the children master the tasks.

STEP 5

Have children copy, solve, and recite the following table:

• 17 + 1 or 1 + 17 = ; therefore 18 - 1 = ; 18 - 17 =
• 16 + 2 or 2 + 16 = ; therefore 18 - 2 = ; 18 - 16 =
• 15 + 3 or 3 + 15 = ; therefore 18 - 3 = ; 18 - 15 =
• 14 + 4 or 4 + 14 = ; therefore 18 - 4 = ; 18 - 14 =
• 13 + 5 or 5 + 13 = ; therefore 18 - 5 = ; 18 - 13 =
• 12 + 6 or 6 + 12 = ; therefore 18 - 6 = ; 18 - 12 =
• 11 + 7 or 7 + 11 = ; therefore 18 - 7 = ; 18 - 11 =
• 10 + 8 or 8 + 10 = ; therefore 18 - 8 = ; 18 - 10 =
• 9 + 9 = ; therefore 18 - 9 =

STEP 6

• Assess mastery by reading aloud the word problems below and having the children mentally compute and recite the solutions. If children have difficulties, repeat the prior phases and then reassess.