If an addend is missing, students use the count-on method or the relationship between addition and subtraction to determine the missing number. Also, they add the addends if the missing number is the sum of the addition sentence. This worksheet, add multiples of 100 and 3-digit numbers, offers a tonne of practice with this idea. As the worksheet uses a horizontal format, it allows for more creativity when it comes to how the student solves the problem. In contrast, in the vertical format, students usually employ the standard method to solve.