# Subtraction Strategies

## Zero Facts

When you subtract 0 from any number, the difference is always the number you started with.     9 - 0 = 9

## Take All

Any number minus itself is always 0.    7 - 7 = 0

## Use Double Facts (Take Half)

You can recognize double facts in subtraction problems.
16 - 8 = ? Think... 8 + 8 = 16

## Use Make 10 Facts

Use addition combinations of 10 to solve subtraction problems from 10.
10 - 6 = ? Think...  6 + ? = 10

## Count Back

When subtracting 1 or 2, you can count back.
8 - 2 = ?  Count back...8, 7, 6

8 - 5 = ? Think...  5 + ? = 8

## Neighbor Facts

The difference between two numbers that live next door to each other is always 1.    10 - 9 = 1         6 - 5 = 1

## Up to 10 and More Facts

Add to the smaller number to make ten. Then add more to reach the larger number. The total amount you add is the difference.
15 - 8= ? Think...  8 + 2 = 10, 10 + 5 = 15  2 + 5 = 7           Therefore...15 - 8 = 7

## Subtraction War

Materials: a deck of cards and small objects such as kidney beans or small blocks

Deal out the entire deck of cards evenly between two players. Face cards can be viewed as the number 10 or can be removed from the deck for the game. Each player turns over the top card from his or her deck. The player with the larger number takes the two cards and as many beans or counters as the difference between the two numbers turned over. Thus, if 6 and 4 are turned over, the player who turned over the 6 gets to take 2 bean because 6-4 = 2. If the same card is turned over by each player, two more cards are turned over and the player with the larger number takes all of the cards and the difference between the larger and smaller number in beans. The game is over when one player has no cards left. The winner is the player with the most beans.

This game can be varied to increase the difficulty by having each player turn over two cards on his or her turn and adding the sum of the cards. The player with the larger sum takes all four cards and the number of beans determined by the difference between the two sums. Thus, if player A turns over a 4 and 6 and player B turns over a 2 and 5, player A takes the cards because 10 is greater than 7. He also takes 3 beans because 10 – 7 = 3.

## Subtraction “Go Fish”

Materials: Flashcards or index cards with subtraction facts written on them but no answers

Each player is dealt 7 cards. Matches or pairs are made by matching differences. Thus 12 - 9 and 8 - 5 can be a match. On a player’s turn, he or she asks another player for a difference that would make a match with a card in his or her hand. Thus if the player has 18 -9 in his hand, he would ask another player for a 9.  If that player has 12 - 3 or any other card equaling 9, a match has been made. Otherwise, the player is told to “Go Fish.”

## Make a Subtraction Problem

Materials: A deck of playing cards

Place 7 cards face side up between the players. The object is to use any 3 cards to make a subtraction problem on your turn. If you are unable to make a problem on your turn, you can remove 3 cards and replace them. Keep taking turns making problems until the cards have all been used or you can no longer make any problems.

## X-Ray Vision

Materials: A paper bag, 2 dice, a number of 12 - 15 objects, paper

Player 1 rolls the dice, adds the numbers and takes that many objects out of the bag. Player 1 tries to figure out what is left in the bag. Both players look in the bag to check. Players than record an equation to match what they just did such as 15 - 9 = 6. Then, player 1 places the objects back in the bag and player 2 goes. Continue switching roles until you have recorded 10 equations.

## Race to Zero

Materials: A die, paper

Both players start at 100. Player 1 rolls the die, decides whether to use the number as a ten or as a one and subtracts the number from 100. (Example: a 3 can be 30 or 3). Player 2 repeats the same steps. Play continues until each player has rolled seven times. The player closer to zero after the seventh round is the winner. If a player reaches zero before the seventh round, the game is over and the other player wins.