Item: tExtendGeometric3b

Stem:

If 5 is the first term, what is the 11th term in the following sequence?

5, 10, 20, 40, 80, ...

Inputs:

1. Enter your answer here:

Key:

• Observable: 5120. Score: 1; Evidence Value: 1.
  • Student:Right!
  • Teacher:The student correctly found the 11th term of a geometric sequence.
• Observable: 160. Score: 0; Evidence Value: 0.
  • Student:That's incorrect, but you are close. You correctly identified the rule for generating successive terms in the sequence, but you found the next term, instead of the 11th term.
  • Teacher:The student found the next term of a geometric sequence, instead of the 11th term.
• Observable: 2560. Score: 0; Evidence Value: 0.
  • Student:That's incorrect, but you are close. You correctly identified the rule for generating successive terms in the sequence, but you found the 10th term, instead of the 11th term.
  • Teacher:The student found the 10th term of a geometric sequence, instead of the 11th term.
• Observable: 10240. Score: 0; Evidence Value: 0.
  • Student:That's incorrect, but you are close. You correctly identified the rule for generating successive terms in the sequence, but you found the 12th term, instead of the 11th term.
  • Teacher:The student found the 12th term of a geometric sequence, instead of the 11th term.
• Observable: 85. Score: 0; Evidence Value: 0.
  • Student:Sorry, that's incorrect. It looks like you found the difference between the first two terms in the sequence, and added this value to the 5th term. But this is a geometric sequence, so you should multiply to find successive terms. Also, you are looking for the 11th term, rather than the next term.
  • Teacher:The student may have misidentified the sequence as arithmetic instead of geometric. Also, the student may have tried to generate the next term, instead of the 11th term.
• Observable: 110. Score: 0; Evidence Value: 0.
  • Student:Sorry, that's incorrect. It looks like you found the difference between the first two terms in the sequence, and added this value to generate successive terms. But this is a geometric sequence, so you should multiply to find successive terms.
  • Teacher:The student may have misidentified the sequence as arithmetic instead of geometric.
• Observable: 2048. Score: 0; Evidence Value: 0.
  • Student:Sorry, that's incorrect. It looks like you correctly recognized that this is a geometric sequence with a common ratio of 2. In fact, you gave the correct answer for the sequence 2, 4, 8, 16, 32,... But this sequence has a starting term of 5.
  • Teacher:The student probably recognizes that this is a geometric sequence with a common ratio of 2, but maynot have considered the importance of the initial term.
• Observable: . Score: 0; Evidence Value: 0.
  • Student:Sorry, that was incorrect.
  • Teacher:The student got this item incorrect.

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