Use compatible numbers to complete this problem. Then estimate the sum.

3,428
+432
_____

What numbers are 3428 and 432 fairly close to? Once you come up with those, then you should be able to add in your head and estimate the answer.

3428 -- fairly close to 3400
432 -- fairly close to 450

When you add those two in your mind, you should get 3850.

3860

To use compatible numbers, we round each number to the nearest multiple of 10, 100, or 1000, depending on the level of accuracy we want.

In this case, let's round each number to the nearest hundred, since all the given numbers are in thousands.

3,428 rounds to 3,400
432 rounds to 400

Now, we can estimate the sum by adding the rounded numbers:

3,400 + 400 = 3,800

Therefore, using compatible numbers, the estimate for the sum is 3,800.