Item: tModelExtendArithmetic2a
Stem:
Alice has a frequent customer card with her favorite ice cream store.
When she first gets her card, the owner of the ice cream store puts 3 stamps
on it. After that, Alice gets 2 stamps on her card each time she buys an ice
cream cone. Once she has earned at least 15 stamps, Alice can exchange her
card for a Super Deluxe Chocolate Peanut Butter sundae.
How many ice cream cones must Alice buy before she can earn the sundae?
Inputs:
- Enter your answer here:
Key:
- Observable: 6.
Score: 1;
Evidence Value: 1.
-
Student:Right!
-
Teacher:The student got this item correct.
- Observable: 15.
Score: 0;
Evidence Value: 0.
-
Student:Sorry, that's incorrect. That's the total number stamps that Alice needs.
Since she started with 3 stamps, she needs fewer than 15 cones. But she also
earns 2 stamps per cone. The correct answer is 6 cones.
-
Teacher:Student probably selected the total number of stamps.
- Observable: 8.
Score: 0;
Evidence Value: 0.
-
Student:Good try, but you didn't figure in the three stamps that Alice started with.
The correct answer is 6 cones.
-
Teacher:Student figured that 2*8=16, enough stamps to get the
free sundae.
- Observable: .
Score: 0;
Evidence Value: 0.
-
Student:Sorry, that was incorrect. Starting with the original 3 stamps, Alice needs
to buy 6 cones to earn the additional 12 stamps (2 stamps per cone)
to bring her to 15.
-
Teacher:The student did not get this item right.
Metadata:
Item Node: tModelExtendArithmetic2a,
Difficulty: 2.
Proficiencies: ModelArithmetic,
ExtendArithmetic.