:Flies at the Barbecue
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Approach: Independent  Level: Year 8
Focus:   Solving an algebraic word problem
Resources: Answer booklet
308KB
Questions / instructions:

At a family barbecue 1 fly arrives in the 1st minute after the meat is put on the barbecue. In the 2nd minute 3 more flies arrive. In the 3rd minute 5 more flies arrive. In the 4th minute 7 more flies arrive. This pattern continues for the whole barbecue.
   
% responses
2005 ('01)
-
Y8
1. How many more flies arrive in the 10th minute?
 
    Show how you work out your answer.
19
52 (46)
    Working out:
    (method, not accuracy)
rule identified (2n-1) or equivalent
4 (2)
adding 2 repeatedly
52 (47)
other appropriate method
8 (10)
2. What is the total number of flies at the barbecue after 10 minutes?
    Show how you work out your answer.
100
26 (18)
    Working out:
    (method, not accuracy)
rule identified (n2) or equivalent
0 (0)
adding the 10 numbers
23 (22)
other appropriate method
6 (9)
3. How many more flies arrive in the 50th minute?  
    Show how you work out your answer.
99
15 (9)
    Working out:
    (method, not accuracy)
rule identified (2n-1) or equivalent
5 (3)
adding 2 repeatedly
6 (4)
other appropriate method
7 (8)
   
Total score:
7–8
3 (2)
 
5–6
9 (8)
3–4
21 (20)
1–2
42 (37)
0
25 (34)
Commentary:
This was a difficult algebra word problem, especially questions 2 and 3. Students in 2005 showed a moderate increase in solving these problems over the 2001 cohort.
 
Chapter Graphic
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