In problem A, how can you use a number line to find the difference?
Answers vary; encourage students to try drawing a number line and to count how much they hop backward or forward.
How can you use friendly numbers to find the difference?
Answers vary; encourage students to use friendly numbers (numbers ending in zero or 5) to subtract. For example: Subtract 3 tens first and then 5 ones.
In problem B, how can you group the numbers to find the sum? What is the sum?
Possible response: Add 21 and 9 to get 30, then add 30 and 35 to get 65. Then, finally add 3 more. The sum is 68.
In problem C, how many ones, tens, and hundreds are there? How can you regroup the ones into tens and ones?
11 ones, 8 tens, and 9 hundreds; regroup the 11 ones into 1 ten and 1 one.
What is the sum?
In problem D, How did Matt solve the problem?
Possible response: He used base-ten blocks to show 6 tens and 5 ones. He took away 3 tens and 9 ones to get 2 tens and 6 ones.
How did Bella solve the problem?
Possible response: She started at 65 and counted back 3 tens and 9 ones to get a total difference of 26.
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