3 Digit Math Addition Worksheets - Academy Simple Example 1: 524 + 416 = 940 In the above operation, we first dealt with the number in the units digit. As we can see, there is a carry-over operation here. Because when we add the numbers 6 and 4 in the units digit, we find the number 10. We wrote the 0 part of this 10 number in the total section below.