Download Task Exemplar 2.NBT.B.9

2.NBT.B.9
Explain why addition and subtraction strategies work, using place
value and the properties of operations (Explanations may be supported
by drawings or objects).
Math Practices:
MP.1: Make sense of problems and preserver in solving them
MP.2: Reason abstractly and quantitatively
MP.3: Construct viable arguments and critique the reasoning of others
MP.4: Model with mathematics
MP.5: Use appropriate tools strategically
MP.6: Attend to precision
MP.7: Look for and make use of structure
Task Exemplar 1:
Daisy bought some things at the pet store for her new puppy. Here is a list of
the things that she bought. Daisy added the prices to make sure that she had
enough money to pay for them. This is how she added the prices.
First Daisy added 8+2=10, “That makes $10 for the bed and the brush” she
said.
Next Daisy added 10+4=14, “Four more for the food makes it $14” she said.
Lastly Daisy added 14+6=20, “Six more for the toy makes it $20. It will cost
$20.00 to buy all of these things” Daisy said.
Why did Daisy add the amount for the bed and the brush as her first
strategy? Explain your thinking using numbers, pictures and words.
Task Exemplar 2:
Moses had the following number cards
.
His teacher asked “What do you get when you add the number cards?”
Moses wrote the following equation 10+7=17
Part A:
Moses’s teacher then asks “If I shuffled the cards and had you add them in a
different order would the total amount still be 17? Explain your thinking
using numbers, pictures and words.
Part B:
Moses’s teacher then asks what if you subtracted the seven number card
from the 10 number card what would the answer be? Explain using numbers,
pictures and words to show how Moses might figure out what the total is
now.
Part C:
Moses’s teacher then asks “What if I took away the ten number card from
the seven number . What would happen and why? Represent your thinking
using numbers, pictures and words.
Part D.
Does subtraction work the same as addition, why or why not? Explain using
what you know about these two operations and how they work together.
Represent your work with numbers, pictures and words.