Number in the Middle
This is one of my favorite addition strategies from Two Plus Two Is Not Five. It is based on addition Doubles facts.
Number in the Middle teaches the addition facts: 2+4, 3+5, 4+6, 5+7, 6+8, 7+9, and 4+2, 5+3, 6+4, 7+5, 8+6, and 9+7.Students must first know the Doubles addition facts: 3+3, 4+4, 5+5, 6+6, 7+7, 8+8.
Be sure to use counters to show why these facts work with Number in the Middle!
Only one number fits in the middle between the numerals in these facts.
(Students need to be able to tell which number comes between, or in the middle.)
2+4 Between 2 and 4 2 3 4 Double 3. 3+3=6. 2+4=6.
3+5 Between 3 and 5 3 4 5 Double 4. 4+4=8 3+5=8.
4+6 Between 4 and 6 4 5 6 Double 5. 5+5=10 4+6=10.
5+7 Between 5 and 7 5 6 7 Double 6. 6+6=12 5+7=12.
6+8 Between 6 and 8 6 7 8 Double 7. 7+7=14 6+8 =14.
7+9 Between 7 and 9 7 8 9 Double 8. 8+8=16 7+9=16.
If your student knows 3+3, then teach 2+4 and 4+2.
Ask, what comes between the numbers: 2 ____ 4, and 4____2.
Why? Show the math fact with counters. Take one off the 4 and put it on the 2. There are two groups of 3, and 3+3=6. What number fits between 2 and 4, or between 4 and 2? Double it.
If your student knows 5+5, then teach 6+4 and 4+6.
Ask, what comes between the numbers: 4 ____ 6, and 6____4.
Why? Show the math fact with counters. Take one off the 6 and put it on the 4. There are two groups of 5, and 5+5=10.
What number fits between 4 and 6, or between 6 and 4? Double it.
Continue to demonstrate using the counters.
If your student knows 6+6, then teach 5+7 and 7+5. What number fits between 5 and 7, or between 7 and 5? Double it.
If your student knows 8+8, then teach 9+7 and 7+9. What number fits between 7 and 9, or between 9 and 7? Double it. (7+9 and 9+7 are also introduced with different strategy called Magic 9. See earlier blogpost.)
If your student knows 4+4, then teach 3+5 or 5+3. What number fits between 3 and 5, or between 5 and 3? Double it.
Written practice for these math facts is in Two Plus Two Is Not Five: Easy Methods to Learn Addition and Subtraction. See sidebar for where to purchase. Let me know if you like this strategy!
See sample pages from the book to learn more strategies.
