Item: tVerbalRuleExamplesTableModelArithmetic3a

Stem:

The rates that Zack charges for babysitting are as follows:

-- $2.50 per hour for the first child, and

-- $0.75 per hour for each additional child.

Fill in the values below to show Zack's hourly charges for babysitting one, two, and three children.

Inputs:

1. 1 child: $
2. 2 children: $
3. 3 children: $

Key:

• Observable: 2.50, 3.25, 4.00. Score: 1; Evidence Value: 1.
  • Student:Right! Your answers, $2.50 per hour, $3.25 per hour, and $4.00 per hour, are correct.
  • Teacher:The student got this item correct.
• Observable: 2.50, 3.25, 3.25. Score: 0; Evidence Value: 0.
  • Student:Sorry, that's not right. Your first two answers, $2.50 per hour and $3.25 per hour, are correct. However, the rate that Zack charges for supervising three children is higher than the rate for supervising two.
  • Teacher:Student added in the 75 cents only for the second child.
• Observable: 3.25, 4.00, 4.75. Score: 0; Evidence Value: 0.
  • Student:You are close, but that's not quite right. It's true that Zack charges an extra $.75 per hour to supervise each additional child, but he only charges $2.50 per hour to supervise one child.
  • Teacher:Student added in the additional charge for the first child, but did everything else right.
• Observable: 3.25, 4.00, 4.00. Score: 0; Evidence Value: 0.
  • Student:Sorry, that's not right. Zack charges $2.50 per hour to supervise one child, and an extra $.75 per hour to supervise each additional child.
  • Teacher:Student added in the additional charge for the first child, added it once more, but then didn't add it for the third child.
• Observable: 2.50, 5.00, 7.50. Score: 0; Evidence Value: 0.
  • Student:Sorry, that's not right. You are correct that Zack charges $2.50 per hour to supervise the first child. But he only charges an extra $.75 per hour to supervise each additional child.
  • Teacher:Student assumed the rate was the same with each additional child.
• Observable: . Score: 0; Evidence Value: 0.
  • Student:Sorry, that's not right. Zack charges $2.50 per hour to supervise one child, and $.75 per hour to supervise each additional child. The correct answers, for one, two, and three children are: $2.50, $3.25, and $4.00.
  • Teacher:The student got this item incorrect.

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