3.OA.B.6 Flawed Reasoning- Division as Unknown Factor

Evidence Statement 3.C.4-2-Distinguish correct explanation/reasoning from that which is flawed, and if there is a flaw in the argument, present correct reasoning.

Marcus's Reasoning

Marcus has 48 pieces of candy to share with 6 friends. 

He wants each friend to get the same amount of candy. 

Marcus thinks he should put 7 pieces of candy into a bag for each friend.

Part A

Marcus is incorrect in his reasoning. 

• What is the error in Marcus' reasoning?

Explain the error in Marcus' reasoning in the space provided.

Part B

Explain how Marcus can correct his reasoning.

Write an equation or your explanation to help Marcus correct his reasoning. 

Student Copy

Scoring Rubric

Part A

Score of 1 Point:

• Reasoning component- the student correctly identify the reasoning error.

Sample student response: Marcus is incorrect because 48÷ 6= 8  not 7.   Or 6 x 7 = 42

 Part B

Score of 2 Points- Student response contains the following 2 elements

• Computation Component- Student correctly solves 48 ÷ 6 = 8  
• Reasoning Component- Student explains that multiplication is the opposite of division. 

Sample Student Response: Marcus could use multiplication to solve the problem. He could use the equation 6 x ? = 48 and find what factor multiplied by 6 has a product of 48.  

Score of 1 Point- Student response contains 1 of the 2 elements.

Score of 0 Points- Student response is incorrect or irrelevant.

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