Multiplying and dividing

Overview

Using this Resource

Connecting to the Curriculum

Marking Student Responses

Working with Students

Further Resources

This task is about finding correct answers to maths problems with mistakes.

Some children made small mistakes in their calculations. In the following questions work out what the correct answer should have been.

Question 1Change answer

a) Sanaj multiplied a number by 2 instead of dividing it by 2. The answer he got was 32.

What should his answer have been?

b) When Sara multiplied a number by 3 instead of dividing it by 3, the answer she got was 36.

What should her answer have been?

c) When Min multiplied a number by 5 instead of dividing it by 5, the answer she got was 100.

What should her answer have been?

Task administration:

This task is completed with pencil and paper or online with auto-marking.

Levels:

3, 4

Curriculum info:

Keywords:

Description of task:

Students work out the correct answers to arithmetic problems given an incorrect solution.

Learning Progression Frameworks

This resource can provide evidence of learning associated with

within the Mathematics Learning Progressions Frameworks.

Answers/responses:

Diagnostic and formative information:

	Common error	Likely reason
a) b) c)	16 12 20	Solved by dividing 'answer' by the divisor, i.e., 16 = 32 ÷ 2, 12 = 36 ÷ 3, 20 = 100 ÷ 5. This gives the original number, not the answer.
c)	25	Multiplies 5 × 5.
	1 or 2 out of 3 correct.	Does most calculation correctly but fails to exploit the close similarity of the questions.