Third Grade Subtraction: Concepts and Sample Problems

Understanding Subtraction for Third Graders

The most important aspect of subtracting 3-digit numbers is formatting. Help your child make sure the ones, tens and hundreds columns are lined up. For instance, in the problem 342 - 105, the 3 should be directly over the 1 in the hundreds place, the 4 should be over the 0 in the tens place, and the 2 should be over the 5 in the ones place.

Formatting is especially important when problems require students to borrow numbers from other columns. Borrowing can be confusing for some students; however, with practice, your child will become familiar with the process. Until then, help him by writing out the steps on a note card so he can keep it nearby at home or in class.

For example, consider the problem 348 - 176. Your child should begin by subtracting the numbers in the ones column (8 - 6 = 2). Then, he should subtract the numbers in the tens column; however, because he can't subtract 4 from 7, he'll have to borrow one from the hundreds column. Have him cross out 3 and write 2 in the hundreds column. Then, have him subtract 14 - 7 = 7. Finally, he can subtract the numbers in the hundreds column (2 - 1 = 1), so the final answer is 172.

Because they're starting to work with larger numbers, third graders may be asked to estimate the difference between two numbers by rounding. For example, to estimate the difference between 765 and 590, they might round the numbers to the nearest hundred. So, 765 would be rounded to 800, and 590 would be rounded to 600. The difference between 800 and 600 is 200, so there's a difference of approximately 200 between the original numbers.

Subtraction Problems and Solutions

1. 783 - 412

Although these are large numbers, this problem is relatively simple because it doesn't require borrowing. The answer is 371.

2. Estimate the difference between 911 and 185.

Begin by rounding the numbers to the nearest hundred (900 and 200). The difference is approximately 700.

3. Solve for x: 187 - x = 94

This type of problem helps kids prepare for algebra in later grades. It also helps them understand the relationship between the numbers in a subtraction problem.

To solve, subtract 94 from 187 (187 - 94 = 93). Encourage your child to always check his or her answer by plugging the number back into the original problem: 187 - 93 = 94.

4. Matthew owes his sister $551. If he gives her $325, how much money does he still owe her?

Subtract 551 - 325. Because you can't subtract 1 - 5, borrow one from the tens column. Then, subtract 11 - 5 = 6. Continue for the tens and hundreds columns. Matthew still owes his sister $226.