# Add and Subtract Within 100: Activities for Second Grade Students

After students have been introduced to beginning math concepts, it is important to reinforce the concepts using a variety of techniques. Make it fun but challenging. Work independently, in small groups or as a whole class. Here are a few ideas to support a second grade objective.

## Objective

Fluently add and subtract within 100 using strategies based on place value, properties of operations, and/or the relationship between addition and subtraction.

MA2-NBT-B-5

## Materials

- Paper
- Pencils
- Rulers
- Hundreds Charts
- Decks of cards (or homemade cards) Numbers 2-10
- Dice
- Spinner with 0-10
- Colored chips
- Index cards

## Number Line Strategy

Use a piece of paper and a ruler to draw a horizontal line across the page to make a number line. Assign each student a two-digit number as the beginning number on the number line and instruct them to make 20 vertical marks and write numbers under each mark until they reach the final number. For example, the student might start at 23 and end at 43.

The game starts with both players placing a chip on the middle number. In our example, that would be 33. The object of the game is to work your way to one end of the number line. The player on the left (Player A) will subtract and the player on the right (Player B) will add.

Let’s say that Player A is on 33 and spins a 5. He would subtract 5 from 33 and place his chip on 28. Player B, who is also on 33, spins and gets 2, so he moves his chip to 35.

As a defensive move, the player may decide to move the opponent’s chip at his turn instead of his own to prevent him from winning. Addition, subtraction and strategy!

## It’s in the Cards

**Target:**A pair of students sits facing each other with a deck of cards in between them. Cards should only have numbers 2 through 10. (No face cards, jokers or aces). Give the students a “Target” number. A player takes a card from the top of the pile and places it face up in front of him in a row. Take turns doing this. Each player has his own row of cards. He adds each number chosen onto his personal total. The player who reaches the target number first is the winner.

**Beat This:**A pair of students sits facing each other with a deck of cards with only numbers 2 through 9. (No aces, face cards or jokers). This time, each player takes two cards and arranges the cards in front of him so that they form the largest possible two-digit number. So a 6 and an eight would be 86. Then decide which of the two students has the biggest number. The student with the biggest number adds his number with his opponent’s number. The opponent takes the two numbers and subtracts. The answers can be used as points for the players or just give one point for the holder of the highest number.

## Hundreds Chart

Point to a number on the hundreds chart and ask how many more till we reach 100. Then, have a “Math Talk” to discuss the strategies that were used. Did you count one number at a time to reach 100? Did you count rows of 10? Did you subtract mentally?

Put your finger on the number 4. Where will you be if you add 9? Did you have to count or did you add mentally? What if you were on 23 and added 9? Can you do that without counting? Observe the students to see who can recognize a pattern on the chart when 9 is added.

Select two teams of students. Use a spinner and the Hundreds Chart. Which team can reach 100 first? If they find an answer without counting they can move forward one extra space.

## Which One Is Not the Same?

Write a number sentence on the board. Then write three number sentences under it making one of them incorrect. For example:

21+ 13

20+ 14 22+ 15 19+15

Have students write their own problems on a file card and trade with a partner. When the two students have solved each other’s cards, they move on to a different partner.

## Roll the Dice

Working with partners or in small groups, each student writes the numbers 1 through 12 on a piece of paper. Each player takes a turn rolling the two dice. The player may choose to add or subtract the amount rolled. Then the player says the math fact and crosses out the answer on his paper. The winner is the one who crosses out every number on his paper. Or you can set a time limit and see who has crossed out the most when time is up.

For example: Player One rolls a 4 and a 2. He says, “4+2= 6”. Then he crosses off the 6 on his paper. But if the six is already crossed off he could say, “4-2=2” and cross out 2.