3.NF.A.3b Comparing Fractions (Flawed Reasoning)

Evidence Statement 3.C.4-4  Distinguish correct explanation from that which is flawed, and if there is a flaw in the argument, present correct reasoning. (For example, some flawed student reasoning is presented and the task is to correct and improve it.)

Pizza For Dinner

McKinley and Delaney had pizza for dinner. The image shows the fraction of a pizza that each girl ate.

The image shows a rectangle divided into 8 equal pieces. 2 of the pieces are shaded in.

The image shows a rectangle divided into four equal pieces. 1 of the pieces is shaded in.

Part A

• How much pizza did McKinley eat?

• How much pizza did Delaney eat?

Enter the fraction of the pizza that each girl ate in the space provided.

Part B

Delaney stated that she ate more pizza than McKinley because she had two pieces and McKinley only had one.

• Delaney is incorrect in her reasoning. 
• Explain why Delaney's reasoning is incorrect. 
• Write a correct comparison for the amount of pizza both girls ate for dinner.

Enter your answer and your work or explanation in the space provided.

Student Copy

Scoring Rubric Part A-

Score of 1

Student response includes a correct fraction for each sandwich that was eaten. (McKinley 1/4  and Delaney 2/8)

Score of 0 

Student response is incorrect or irrelevant.

Scoring Rubric Part B

Score of 2- Student response includes the following 2 elements.

• Reasoning Component = 1 point. The student explains why Dalaney's reasoning is correct. ( Sample Response- I know that McKinley and Delaney ate the same amount of because the same sized region. The fractions are equivalent because they ate the same size of the whole.)

• Computation Component = 1 point.  The student provides a correct comparison of the amount of pizza that McKinley and Delaney ate: 1/4  =  2/8

The image shows a rectangle divided into 4 equal pieces. 2 of the pieces are shaded in.