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Turn-Around Rule
Nila and Alexis thought of two more ways to show how to multiply 3 20.
- Use Nila's or Alexis's way to find these products.
- 2 70
- 4 50
- 9 80
Alexis wants to make a different banner to hang on the door. “This one should be tall and skinny. Let's make 20 rows of 3 stars this time.”
“That's 20 3. So how many is that?” asked Irma.
“The answer is the same as 3 20,” said Alexis. “That's because we can switch the order of the factors and the answer stays the same. So both banners have 60 stars.”
“That makes sense,” said Nila. “If you turn the banner with 20 rows of 3 stars on its side, it looks just like the banner with 3 rows of 20 stars.”
Alexis used the turn-around rule. Mathematicians call this the commutative property.
- Use the turn-around rule with Nila's or Alexis's way to find these products.
- 70 2
- 50 4
- 80 9
- 60 9
- 80 5
- 20 5