standard_description: Apply properties of operations as strategies to multiply and divide. (Students need not use formal terms for these properties.) ^( )Examples: If 6 × 4 = 24 is known, then 4 × 6 = 24 is also known. (Commutative property of multiplication.) 3 × 5 × 2 can be found by 3 × 5 = 15, then 15 × 2 = 30, or by 5 × 2 = 10, then 3 × 10 = 30. (Associative property of multiplication.) Knowing that 8 × 5 = 40 and 8 × 2 = 16, one can find 8 × 7 as 8 × (5 + 2) = (8 × 5) + (8 × 2) = 40 + 16 = 56. (Distributive property.)
problem_activity: Problem 1
Estimate the mass of the following objects in grams or kilograms, depending on which is more appropriate. Then measure their actual mass using your tool(s).
a.   Pair of scissors
b.   Thumbtack
c.   Ruler
d.   Textbook
Problem 2
What is the mass of each of the following objects, according to the reading on the scale? For any measurement that isn’t exact, make your best estimate.
a.
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b.
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c.
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aligns: no