Today I will connect to prior knowledge to start students off. I display a 2-digit number in base 10 blocks and ask students to write that number in their math journal. We check the number together. I ask students if they can show the same number using coins. I have them draw the coins in their journals and ask 1 student to draw it for us on the board. Today I keep the numbers to ones that can be built with dimes and pennies to reinforce tens and ones. I ask them to only use dimes and pennies to make 13cents, 41 cents, 64 cents.
Next I ask students what 10 cents more would be than each of the numbers ? I ask them to write the new number. We discuss which place changed (the tens place - they just added 1 dime).
I do another example with a 2-digit number and then I present a 3-digit number. I ask them to build 241 with base ten blocks. Now I ask them to think about that number in money. What would it be in pennies? (241 pennies) How do we usually read that amount? ( 2 dollars and forty one cents.). "Yes, we break the number up into dollars and cents when we go from pennies to $2.41. Are they the worth the same amount? (Yes) We work through the same process of writing several more numbers, showing the amount with dollars and coins and discussing what we have done.
I present one more example and then have students put their journals away so they are ready for the lesson.
Today I tell students that the purpose of the lesson is for students to be able to add and subtract using dimes and dollars. I tell them that they will be working in 3 small groups to practice our adding and subtracting.
The first group will play a game called EASY COME! EASY GO!. In this game the students will work in partners. They will take turns rolling two dice and taking that number of pennies, or dimes. Each time they roll they will add on. They can not have more than 9 of any one coin on their board at any one time. They must trade for the next coin. When they reach $1.00 they start subtracting. They play until one of the partners reaches 0 again. Students are modeling with mathematics as they count out the coins and trade in. (MP4)
The second group will work independently to figure out ten more and ten less than the number they make by drawing 2 number cards from a deck. The student draws 2 cards and writes the number in the center of the top line of the paper. They may build the number in either order as long as they still have a 2 digit number (in other words they can't form 02 because ten less would be negative, but if they drew a 1 and a 2 they could form 12 or 21) On the left they will write the number that is 10 less and on the right they will write the number that is 10 more. They will then put those cards back and draw 2 new cards and start again. Students must understand the structure of numbers, especially if they draw a 0 as they write the numbers and then think of how to change the number to ten more or ten less. (MP7)
The third group will make a picture of an object to sell. They will give it a price less than 1.00. They will then play a game where they pick a card from the objects drawn and then pick a what to do card. The cards say "SALE TODAY PAY 10 CENTS LESS" "PRICE INCREASE PAY 20 CENTS MORE TODAY" etc. The student has to figure out the new price and pay the store (a pot in the middle) for their object using exact change. Students are making sense of the idea of the sale cards and solving the problems (MP1) Students take turns buying the objects and returning the cards to the pile.
After I make sure each group is settled I set the timer for 10 minutes of work and then I circulate around listening, questioning and helping in any center that is needed. After 10 minutes I ring the bell and direct students to move to the next center. Again I settle students in and then observe.
I ask students to return to their seats. I have them take out their math journals and write the amount $2.46 in their books. I ask them to circle it. Next I ask them to write $1.00 more, $3.00 more, 10 cents less and 30 cents less.
I circulate around and check for understanding.