Homework Headache: Using Number Bonds
For this week’s homework headache, we chose an example that has recently made the rounds as a common source of common core math confusion. The problem asks the student to use “Number Bonds” to add.
Since it is easier to add a 1-digit number to 10 than two 1-digit numbers whose sum is greater than 10, this problem asks you to break up numbers into smaller parts so you can create 10 and then add what is left over. For most of us, this might seem a bit silly; particularly since as adults we can pretty quickly figure out that 8 + 7 is 15 in our heads.
For many of our kids, however, this mental calculation does not come as naturally. Therefore, if our kids can learn to break down smaller numbers into something that equals 10 their Mental Math may improve.
Now let’s get started. In the first example, 8 + 7 you are given two circles below the 7. This means you need to break up the 7 into two smaller numbers. Since we are trying to make the 8 into a 10 in order to do the mental calculation, the first number should be the difference between 8 and 10. In other words, ask yourself, what do you need to add to 8 to get to 10. The answer is 2 so in the first circle under the 7 write a 2.
7 – 2 equal 5 so place a 5 in the second circle below the 7. Now when you add the numbers up you can just add 10 to the number in the second circle. 10 + 5 = 15.
Now let’s go through one more example on the upper row together.
In this example, first ask yourself how do you turn 6 into a 10. Since 6 + 4 =10, write a 4 in the first circle. Next, complete the second circle by subtracting 4 from 5 to get 1. 6 + 5 is equivalent to 10 + 1, but conceptually it is much easier to see that 10 + 1 = 11 rather than 5 + 6.
Here are the answers to the other examples on the top row:
Ask your child what number plus 7 equals 10. Since 7 + 3 =10, record that 3. Next subtract 3 from 6. 6 – 3 = 3. Record a 3 in the second circle.
9 plus what number equals 10? Since 9 + 1 =10, record that 1 in the first circle. Next subtract 1 from 5. 5 – 1 = 4. Record a 4 in the second circle.
Need more help? For more complicated problems using Mental Math see our Mental Math Videos in the Homework Unlocked lesson library.
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