# 3.NF.A.3b Comparing Fractions_Pizza for Dinner

## 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.

### 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.