standard_description: Add within 100, including adding a two-digit number and a one-digit number, and adding a two-digit number and a multiple of 10, using concrete models or drawings and strategies based on place value, properties of operations, and/or the relationship between addition and subtraction; relate the strategy to a written method and explain the reasoning used. Understand that in adding two-digit numbers, one adds tens and tens, ones and ones; and sometimes it is necessary to compose a ten.
problem_activity: Problem 1
Elena and Zack want some change to buy penny candy. Their mom keeps rolls of 10 pennies to give to them for just this purpose. Their mom gives them 5 rolls and 4 loose pennies. How can Zack and Elena split the change they got from their mom evenly?
Problem 2
Elena used base-ten diagrams to find 3.72 ÷ 3. She started by representing 3.72.
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She made three groups, each with 1 one. Then, she put the tenths and hundredths in each of the three groups. Here is her diagram for 3.72 ÷ 3.
[IMG]
Elena’s diagram for 3.72 has 7 tenths. The one for 3.72 ÷ 3 has only 6 tenths. Why?
Where did the extra hundredths (small squares) come from?
How would Elena calculate 95.6 ÷ 4?
Problem 3
Andre calculated 95.6 ÷ 4 using a method that was different from Elena’s method.
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Andre subtracted 80.0 from 95.6. What does the 80 represent?
Andre wrote 3.0 above the 20.0 and then subtracted 12.0 from 15.6. How is the 12.0 related to the 3.0?
What do the numbers 20.0, 3.0, and 0.9 represent?
What is the meaning of the 0.0 at the bottom of Andre’s work?
Problem 4
Solve. Show or explain your work.
0.96 ÷ 6 = ___________
9.85 ÷ 5 = ___________
24.08 ÷ 8 = ___________
64.8 ÷ 6 = ___________


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