5th Grade - Adding and Subtracting Large Numbers

Next week, our fifth graders will continue using different strategies to add and subtract large numbers.

Let's look at some different strategies to solve the problem 892 - 567.

• Subtracting in Parts - Start with 892 and subtract 500 (892 - 500 = 392). Next, subtract the tens place (392 - 60 = 332). Finally, subtract the ones place (332 - 7 = 325).
• Adding Up - For this strategy, start with 567 and add up until you get to 892 (567 + 33 = 600 and 600 + 292 = 892). Finally, add your numbers to get the final answer (33 + 292 = 325).
• Subtracting Back - For this strategy, start with 892 and subtract back until you get 567 (892 - 92 = 800 and 800 - 200 = 600 and 600 - 33 = 567). Finally, add your numbers to get the final answer (92 + 200 + 33 = 325).
• Changing the numbers to make an easier problem. For this strategy, it is important to remember that if you change one number you must also change the second number. Imagine you have 84 pennies and your brother has 55 pennies and you want to find the difference. What would happen if both of you got an additional 6 pennies? The difference would still be the same. Using this idea, we can change 892 into 900, but we must also change 567 into 575 (we added 8 to each number). Now we can use one of our first three strategies to solve this problem (575 + 25 = 600 and 600 + 300 = 900, so 25 + 300 = 325).