If a minuend or subtrahend is missing, students use the count-back method or the relationship between addition and subtraction to determine the missing number. Also, they subtract the numbers if the missing number is the difference of the subtraction sentence. This subtract multiples of 100 from 3-digit numbers worksheet offers a tonne of practice with this idea. This worksheet is about practicing with the horizontal format in which numbers are written side by side. To develop flexibility with numbers and operations, students need to have enough practice in this format and not just rely on the vertical/column method.