Subtract Using Addition

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Subtract Using Addition
CCSS.MATH.CONTENT.2.OA.A.1

Basics on the topic Subtract Using Addition

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What do you learn about subtracting using addition?

When solving subtraction problems, you can us addition to subtract. There are many tools and strategies to solve addition problems, one of which is using a number line! When using addition to solve subtraction problems...

  • Start by creating a new addition equation using what you know from the subtraction equation.

  • Next, put the smaller addend on the left side of the number line.

  • Then, count up the bigger number in the equation. You can do this by counting forward small amounts, like by fives or tens!

  • Finally, find your sum by looking at how much you counted to get to the second number. Remember, the answer to the addition equation is also the answer to your subtraction equation!

Transcript Subtract Using Addition

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 "subtract using addition on a number line" to help figure out how many will be left over. There are many strategies for addition, but what about subtraction? Let's use adding to help us solve subtraction equations. When subtracting using addition… always 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. They brought him twenty-six pieces in total, but he only needs fourteen pieces. We can take this equation and FLIP IT AROUND to use addition! Start with the smaller number, here it is fourteen. Now we need to find the second piece, one way is by using a number line. Put the smaller number on the LEFT side of the number line. Next, count up until we get to the answer, here it is twenty-six. Count with me! five (...) ten (...) if we count up another five we will go past the answer so we can just count up two. Finally, the amount that we counted forward is the answer! Fourteen plus twelve equals twenty-six. If we flip it back to the subtraction equation (...) 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 Mr. Squeaks only needs nineteen. How many scraps will he have left over? Start by flipping the equation from subtraction to addition. Begin with the smaller number, here it is nineteen. Count up using a number line to help find the second part. Remember to ALWAYS put the smaller number on the LEFT side of the number line. Next, skip count until we get to the answer (...) let's skip count together! ten (...) twenty (...) if we count by another ten we will go past, so we can count by ones until we get to forty-five. one (...) two (...) three (...) four (...) five (...) 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 was bits of toothpicks to bend into the steering wheel. If they brought sixty-three bits and Mr. Squeaks only needed twenty-eight, how many will be left over? We can subtract using addition! Start by flipping the equation from subtraction to addition. Next, find the missing second part by using a number line. Always start by putting the smaller number on the LEFT. Then, skip count forward until we reach the answer. The amount that we counted forward is the result of both the addition AND subtraction equation! Twenty-eight plus thirty-five equals sixty-three. That means that sixty-three minus twenty-eight equals thirty-five. Before we see that magical trip, let's review. When subtracting using addition… create a new addition equation. Next, put the smaller number on the LEFT side of the number line Then, count up to the larger number. Finally, the amount you counted up 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?!