Subtract Using Addition on a Number Line

Mr. Squeaks and Imani are building a boat. However, Imani has brought him too many items! Mr. Squeaks needs to subtract from the items. He can solve subtractions by counting on to work out how many items will be left over. Addition and subtraction are inverse, they are opposite operations. That means that we can use addition to solve a subtraction question. Let's use addition to solve some subtraction equations. When we solve a subtraction by counting on, or using addition we need to start by creating an addition equation. Then we can fill in what we know. Imani has brought Mr. Squeaks bits of plastic to build the frame of the boat. Imani brought him twenty-six pieces in total, but he only needs fourteen pieces. We can take this equation and use the inverse to find how many pieces they would have left over. Start with the smaller number, here it is fourteen. Fourteen plus something equals twenty six. To find our missing value put the smaller number on the left side of the number line and the larger number on the right side of the number line. Then, count up in steps until we reach twenty six. Here we can jump five, then another five, then one,then another one until we reach twenty six. How much have we jumped altogether? We have jumped twelve. Fourteen plus twelve equals twenty six. We can rearrange this equation to show twenty six minus fourteen equals twelve. Next, Imani brought Mr. Squeaks scraps of fabric for a flag! They brought Mr. Squeaks forty-five scraps of fabric, but he only needs nineteen. How many scraps will he have left over? Start by using the inverse to rewrite the subtraction problem as an addition with a missing value. Nineteen plus something equals forty five. Begin with the smaller number, here it is nineteen. Count up using a number line. Remember to always put the smaller number on the left side of the number line. Next, we count forward in steps until we reach forty five! Ten, twenty, twenty five, twenty six! Finally, the amount we counted forward, twenty-six, is the answer! Nineteen plus twenty-six equals forty-five. That means that forty-five minus nineteen equals twenty-six. The last thing Imani brought Mr. Squeaks were some toothpicks to make into the steering wheel. If they brought sixty-three toothpicks and Mr. Squeaks only needed twenty-eight, how many will be left over? We can solve the subtraction by using the inverse and counting on using the number line. Start by rewriting the equation as an addition with a missing value. Next, use a number line to count forward between the two amounts. Always start by putting the smaller number on the left. Then, count forward in steps until we reach the larger number. Add up the steps to see how far we have jumped forward. Ten, twenty, thirty, five. We have jumped forward thirty five. So this is our answer. Twenty-eight plus thirty-five equals sixty-three. Or if we re-arrange our equation, sixty-three minus twenty-eight equals thirty-five. Before we see that magical trip, let's review. When solving subtractions by counting on using a number line, rewrite the equation as an addition with a missing value. Next, put the smaller number on the left side of the number line. Then, count up to the larger number. Finally, add up the jumps to see how much was counted on in total. This is the answer! Now, let's see that trip! "It's working, Imani! We did such a great job, but why do I feel like I'm missing something? "Wait, hang on, Imani?!”