Wednesday, July 9, 2008

Math problems of the week: grade 3 Investigations vs. French Math

1. From Landmarks in the Hundreds, a student activity public for grade 3 Investigations (TERC):

Calculator Skip Counting

Choose a number to count by. Pick one you think will land exactly on 300. 
Skip count by this number on your calculator.
Does it work?  If so, write how many of your number it takes to get to 300.

Numbers Did you land on If it worked:
we tried 300 exactly? How many in 300
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______________ Yes No ________________
______________ Yes No ________________
______________ Yes No ________________
______________ Yes No ________________
______________ Yes No ________________

... (18 iterations in all)


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2. From Cahier d'activités mathématiques, CE2 (3rd grade), translated from the French:

Goal:  Calculate in your head. 

Observe:  

32 x 4 = 32 x 2 x 2
32 x 4 = 64 x 2
32 x 4 = 128
32 x 40 = 1280


5 is half of 10
12 x 5 is half of 12 x 10
12 x 10 is 120
12 x 5 is 60

50 is half of 100
12 x 50 is half of 12 x 100
12 x 100 is 1200
12 x 50 is 600

1. Solve in your head:

43 x 2 = _____ 82 x 2 = _____ 16 x 10 = _____ 35 x 10 = _____
43 x 4 = _____ 82 x 4  = _____ 16 x 5 = _____ 35 x 5 =  _____


2. Solve in your head:

24 x 4 =  _____ 43 x 4 =  _____ 23 x 5  = _____ 74 x 5  = _____
24 x 40 = _____43 x 40 = _____23 x 50 = _____74 x 50 = _____

3.  Solve in your head:

33 x 4 =   _____ 13 x 40 = _____ 26 x 5 = _____ 14 x 50 = _____
120 x 4 = _____ 21 x 40 = _____ 31 x 5 = _____ 15 x 50 = _____

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Which is more "rote" and "mindless," mental math, or skip counting on a calculator?

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