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
In a marching band there are 24 trombones and 15 snare drums.
Heather says, “The ratio of trombones to snare drums is 24:15.” Audrey says, “No, the ratio of trombones to snare drums is 8:5.” Who is right and why?
Problem 2
You are making a mixed bag of walnuts and cashews. The ratio of the number of walnuts to the number of cashews you want to use is 5:6. You have 54 cashews to include in the mix. How many walnuts should you add? Justify your answer by showing that the new ratio you created of the number of walnuts to cashews is equivalent to 5:6.
Problem 3
Which of the ratios in the list below are equivalent to the ratio 12:8? Explain or show how you know each ratio is equivalent.
a.   8:12
b.   3:2
c.   2:3
d.   24:16
e.   6:4
f.   6:2
g.   15:10
h.   20:16


aligns: no