Subtracting multiples of 10

1.NBT.6 Subtract multiples of 10 in the range 10-90 from multiples of 10 in the range of 10-90 (positive or zero differences), using concrete model 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. Students use concrete models, drawings and place value strategies to subtract multiples of 10. Students can use a number line or hundreds chart.

Ruby has 50 books that she wants to read over the summer Ruby has 50 books that she wants to read over the summer. She has read 20. How many more books does Ruby have to read? Students can use concrete materials such as 10 frame, manipulatives, and base ten blocks to solve. Have several students with different strategies share how they solved the problem.

Can Kala solve this problem using ten frames? 50 -20 = 30 Students can use ten frame, drawings and manipulatives to solve. Students can visualize using a ten frame. Higher level students may count backwards.

Can Colby solve this problem using a number line? 50 – 20 = 30 20 30 40 50 20 + 30 = 50 Students can use drawings and strategies to solve. Relate the strategy to a written method and be able to explain the reasoning used. Use simplified numbers such as 3+2 or 5-2 to model this idea. Ask how counting and addition are alike. Ask how subtracting and counting backwards are alike, 20 30 40 50

Which ways show 50 - 20 = 30 1. 2. 20 + ? = 50 3. 1 and 2 are both correct. 2 is an example of relationship between addition and subtraction. Ask the number sentence that 3 represents 50-30. 20 30 40 50

Rosa solved it this way: There are 40 flowers in the vase at the store. Rosa bought 20 flowers to give to her mom for her birthday. How many flowers are left in the vase? Rosa solved it this way: Is this correct? Agree or Disagree Ask the same question but now use 20 flowers in a vase and 10 were given to Mom. If 40 flowers are left in a vase at a store and Rosa bought 10 of them, how many flowers were there originally in the vase before Rosa made her purchase? 40 – 20 = 20

Juan solves his problem this way: Juan bought 70 pieces of candy to share with his friends. He decides to give 50 pieces of candy away. Juan solves his problem this way: 50 + 70 = 120 20 110 50 80 40 30 60 70 90 100 120 Is this correct? Agree or Disagree This problem goes above the standards range of 90. Higher level students will see the pattern of the number system and be able to go past 90.

Leo solved the problem this way: Leo found 40 pennies in the park. He decided to share them with his friend Mike. Leo gave Mike 10 pennies. How many pennies does Leo have now? Leo solved the problem this way: Is this correct? Agree or Disagree Students can use manipulatives, ten frame and hundreds chart. Students can use what they know 4-3 = 1. Students can count by 10’s. Can students explain verbally how they solved the problem? 40 – 30 = 10

The clown had some balloons. He gave away 30 balloons The clown had some balloons. He gave away 30 balloons. Now the clown has 40 balloons. How many balloons did the clown have? The clown solved the problem this way: 30 60 50 40 70 80 Brainstorm and write all the possible ways to solve this problem. Have a discussion on what is the easiest way to solve the problem. Students can use a number line or a hundreds chart. Students can explain in writing or verbally the method they used. Is the clown correct?

Use your Number Line to Show: 60 – 10 = 50 90 30 60 20 10 40 50 70 80 100 Children need repeated exposure to and practice with counting sequences in order to become fluent with counting. Work with a partner, discuss your method of counting Count by 10’s (forward and backward) For students with difficulties use 6-1= 5 to simplify.

Use your Number Line to Show: 90 – 50 = 40 90 30 60 20 10 40 50 70 80 100 Ask how 50 + 40 can help you solve 90-50.

Use your Number Line to Show: 30 – 30 = 0 90 30 60 20 10 40 50 70 80 100 Zero is a difficult concept for some students. Ask questions such as 60-0, 20-0, 40-40, 80-80 to assess who has a solid understanding of the zero property.

Use a double Number Line to Show: 100 – 70 = 30 100 = 70 + 30 90 30 60 20 10 40 50 70 80 100 90 30 60 20 10 40 50 70 80 100

Dan spent 40¢ on lunch. What do you think he bought? Hot dog 30¢ Apple 10¢ Ice cream cone 10¢ Drink 20¢ Dan spent 40¢ on lunch. What do you think he bought? What are the possible answers? Can Dan buy 2 hot dogs? What three items can Dan purchase with 40 cents? Can Dan purchase all 4 items?