Secret Message

*Get to know your PLANNER and use it as a great resource.

If you have read my Math page on our 5th grade website, write the words: "Math Rules" in your child's Planner in the "Comment Section". Students know to put any notes in the apple box. I wonder how many planners I will see!!

Compitable Numbes are Easy to Compute Mentally

Compatible Number Division Problems:

We like to call Compatible Numbers numbers that "get along" with each other, much like compatible people. In math, we're talking about one number that is easily divisible by another number. These numbers are useful for determining an estimate of the actual answer to a division problem. You will see three different types of Compatible Number problems in homework and on tests:

Type 1: 3792 ÷ 6 = n

The divisor in this problem is 6. Because we know the multiples of 6 without having to work them out, we want to make the dividend (3792) into a number that "gets along" or works easily with the divisor 6. We know that the two largest place values create the number 3700. This number is not a multiple of 6, but 3600, which is very close, is. In this case, we would round the dividend to 3600 and keep the divisor 6 as it is:

3600 ÷ 6 = n
This problem is quickly solved when we use the inverse operation, multiplication: 6 x 6 = 36, so 6 x 600 = 3600.

The actual answer to this problem is 632, so our estimate of 600 is reasonable.

Type 2: 3792 ÷ 60 = n

Much like the problem above, the divisor, 60, is easy to use. Since we know the multiples of 6 without having to work them out, we can also determine the multiples of 60 without much effort. Again, we will keep the divisor the same and round the dividend to the nearest landmark multiple of 60.

3600 ÷ 60 = n

Using the inverse operation, we know that our estimate would be

60 x 60 = 3600.

The actual answer to this problem is 63.2, so our estimate of 60 is reasonable.

Type 3: 3792 ÷ 63 = n

In this problem, we do not readily know the multiples of 63. In this case, we must first round the divisor 63 to the nearest landmark number, which is 60. Now, we can look at the dividend to think of a landmark multiple of 60 that is close to 3792. Of course, the number would be 3600. Using the inverse operation, we can quickly determine an estimate for our actual problem:

60 x 60 = 3600

Again, our estimate would be 60. Since the actual answer is 60.19. Our estimate is very close to the actual answer.