## Sunday, October 19, 2008

### FCTM: Computational Fluency in Subtraction

By: Ashley Russell

The second session that we went to on Friday was a session called "Computational Fluency in Subtraction" presented by Ms. Pat Evans.  In this session, Melissa Ross and I got many different ideas for ways to help our students become more fluent with their subtraction combinations (aka "facts").  Although there were many good ideas, Melissa and I particularly liked the following two activities.

Bump Minus 1
Materials: Bump! Minus One game board, one number cube (with numerals 3-8), 10 linking cubes of two different colors (each student uses a different color)
Directions:
1.Pass out game boards; one per every two players. Players need to decide who will go first by a roll of the dot cube. Lowest number starts the game.
2. First player will roll the cube and place the linking cube on the number rolled MINUS one. For example, if a 4 is rolled the child would say 4-1=3, and place the linking cube on the circle with the 3 inside it.
3. The second player repeats this and play goes on the same way until one of the players rolls a number that is covered by the other player. S/he may then "BUMP" the opposing player's cube off the number and place his/her cube on that number.
4. A number may be "frozen" (cannot be bumped) by the same child rolling the number twice during the game, thus stacking two of the same colored cubes on that number.
5. The game is over when all the numbers are "frozen" or when a player's linking cubes are all used.
**This game could easily be extended by changing the numbers on the cube or on the game board.

Card Magic
Materials: Deck of playing cards (remove tens and face cards, aces represent 1)
Directions: The student removes one card, does NOT look at it, and places it face down, off to the side. Lay out the cards, face up, to resemble a 2-D pyramid.
The remaining card are held in a "deck." The student then finds sums of ten within the displayed cards and removes them, placing them in a "discard" pile. As two cards are removed, two more cards from the deck replace the used cards. The student continues to find sums of ten until all deck cards are used. One card will remain unused. The student must then find the missing addend for the sum of the last ten by "magically" knowing the number that is on the card that was placed face down at the beginning of the game. For example, if the remaining card is a 7, the "Magic" card will be a 3!

This game was so much fun! It is also wonderful practice for combinations of 10 which is an essential skill that all students must master. Plus, the element of "magic" will be sure to lure any student.