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# Add and Subtract with Dimes

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This lesson can be used as a pre-lesson for the Math Mind Magic lesson plan.
This lesson can be used as a pre-lesson for the Math Mind Magic lesson plan.

Students will identify 10 more or 10 less than a given two-digit number within 100.

##### Language

Students will be able to use visuals to explain the steps to name the number 10 more or 10 less than a given two-digit number within 100.

(5 minutes)
• Ask students to raise their hands if they like stickers. Give students time to describe their favorite sticker to a partner. Show a few examples of different stickers.
• Tell students that you are happy because you know a store where they sell stickers for 10Â¢.
• Show students a real or plastic dime, and ask them how much it is worth (10 cents). Think aloud, "With one dime, or 10 cents, I could buy one sticker."
• Show students a real or plastic penny, and ask them how much it is worth (1 cent). Think aloud, "With 10 pennies, or 10 cents, I could buy one sticker. Ten pennies are worth the same amount as one dime."
(5 minutes)
• Create an anchor chart. Write "dime - 10Â¢", and then draw a circle with the letter D inside of it to represent one dime.
• Write "penny - 1Â¢", and then draw a penny with a letter P inside of it to represent one penny.
• Show students a mix of dimes and pennies on the document camera, for example 54Â¢. Count by tens and ones to agree that the total amount of change is 54Â¢. Draw five circles with Ds and four with Ps on the board.
• Say, "I just bought one sticker that cost 10Â¢." Remove a dime, and cross off one D circle on the board. Ask students how much money you have left.
• Ask students to explain their thinking. Show that you can count back one at a time to 44, or subtract one 10. Subtracting one 10 is faster. Count by multiples of 10 to count the dimes, and then ones to count the pennies, to show that you have 44 cents left.
• Draw a two-digit place value chart on the board and label it "tens" and "ones." Show the number 54 as five tens and four ones. Show students that when you subtract one 10, the number becomes four tens and four ones.
• Continue, adding and subtracting dimes. Have students call out the number that is 10 more or 10 less than a given number. Model showing the changes with plastic coins, sketches of dimes and pennies, and on the place value chart.
(10 minutes)
• Distribute personal whiteboards and markers to students. Tell them they will draw dimes and pennies to solve problems.
• Tell students, "I have 48 cents. How many tens are in 48? (Four). How many ones are in 48? (Eight.) How many dimes should I draw? (Direct students to draw four circles with the letter D inside on their whiteboards to represent the dimes.) How many pennies should I draw?" (Direct students to draw eight circles with the letter P inside on their whiteboards to represent the pennies.)
• Continue, "My friends give me 10 more cents. How much money do I have now?" Instruct students to draw one more dime, and count chorally by tens and ones to solve the problem. Display the sentence frame, "You have ____ cents." Prompt students to respond chorally using a complete sentence, "You have 58 cents."
• Instruct students to erase their whiteboards. Continue with a different problem, "I have 32Â¢. (Students sketch dimes and pennies). I buy a sticker for 10Â¢ (Students erase one dime). How much money do I have left?" (Students count chorally by tens and ones and answer with a complete sentence, "You have 22Â¢.")
• Continue with a few more examples of situations that involve earning and spending dimes. Instruct students to sketch the solution as dimes and pennies on their whiteboards.
• Tell students that they will now solve word problems about money.
• Create a chart with the class to review the steps for solving word problems with sketches of dimes and pennies:
• 1) Read the problem and think about what is happening (sketch a stick figure with a thought bubble).
• 2) Underline important words in the problem (write common math terms such as more, less, and all together).
• 3) Sketch dimes and pennies to solve the problem (sketch a circle with a D and write 10Â¢ next to it, sketch a circle with a P and write 1Â¢ next to it).
(10 minutes)
• Distribute the Dime Word Problems worksheet to students.
• Read the problems chorally, and check for understanding of the situations presented in the problems. Model following the steps to solve a word problem, and solve the first problem on the worksheet as a class. Excuse students to finish the remaining problems independently.
• As students finish, challenge them to write a word problem about money on the back of their paper.

Beginning

• Complete the worksheet in a teacher-led small group.
• Act out the word problems using real or plastic coins to improve understanding of the context of the problem.

• Display a hundreds chart for reference as students calculate multiples of 10 more or 10 less than a given number.
• Encourage students to show more than one way to solve the same problem, and to justify their answer.
(5 minutes)
• Circulate as students complete the worksheet and observe that they are able to draw an accurate number of pennies and dimes, and correctly solve for 10 more or 10 less.
• Check that students are not counting by ones to add or subtract multiples of 10. Reteach strategies for mentally finding 10 more or 10 less than a given number as needed.
• As students work on the word problems, prompt them to verbalize their thinking. Check that they understand whether the problems call for addition or subtraction. Ask students to describe a strategy for identifying the number 10 more or 10 less than a given number.
(5 minutes)
• Address any common errors on the worksheet with students.
• Invite students to share other strategies for mentally calculating 10 more or 10 less than a number, for example jumping on a number line, using a hundreds chart or sketching base-ten blocks.
• If time allows, choose students who finished the worksheet early to share a self-created word problem for the class to solve.

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