standard_description: Fluently add and subtract within 20 using mental strategies. (See standard 1.OA.6 for a list of mental strategies.) By end of Grade 2, know from memory all sums of two one-digit numbers.
problem_activity: Problem 1
Solve the following problems. Think about the main differences between each one.
a.   A teacher has 21 batteries. Each calculator uses 4 batteries. How many calculators can the teacher fill with batteries?
b.   Four children can ride in a car. How many cars are needed to take 21 children to the museum?
c.   Ms. Cole wants to share 21 pieces of candy with 4 students. If Ms. Cole gets to eat the pieces of candy that can’t be split evenly, how many pieces of candy will Ms. Cole get?
Problem 2
a.   Mr. Janssen buys a plant at a gardening center. A flower blooms on the plant every seventh day. How many flowers are on his plant after 25 days?
b.   Sean is switching bedrooms with his brother and needs to pack 28 toys into small boxes. He packs 5 toys in each box. How many boxes does he need?
c.   It takes 8 cups of flour to make a cake. I have 35 cups of flour. If I make as many cakes as possible, how many cups of flour will I have left over? How many more cups of flour would I need to be able to make another cake?


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