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Compact Method for Multiplication
Nicholas and Jacob visit Marcie's Pet Store to buy some fish for a new fish tank in Mr. Moreno's classroom. The store has separate tanks so that each kind of fish can live in water with the right conditions.
Marcie's Pet Store has 5 large tanks that hold 315 gallons of water each. Nicholas and Jacob want to figure out how much water is in all of the tanks combined.
Jacob solved the problem by using the all-partials method. Nicholas said he had a shortcut way of computing the product.
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- Review Jacob's method. Tell what he multiplied to find his answer.
Nicholas began by multiplying 5 5 = 25. Nicholas knows this is 2 tens and 5 ones. The small 2 Nicholas wrote above the tens column is called a carry. It reminds Nicholas to add 2 tens in the next step. Nicholas then multiplied 5 1 ten = 5 tens and then he added the extra 2 tens to get 7 tens. Last, Nicholas multiplied 5 3 hundreds = 15 hundreds or 1500.
- How are Jacob's and Nicholas's methods alike? How are they different?
- Do you prefer Jacob's method or Nicholas's method? Why?