Subtracting Across Zeros

Contributor: Erika Wargo. Lesson ID: 12640

If you need $5 and you have $0, what might you do? You could borrow from your neighbor. The same is true in subtraction: If you have to subtract from 0, you can "borrow" a number from its neighbor!

categories

Elementary

subject
Math
learning style
Visual
personality style
Beaver
Grade Level
Intermediate (3-5)
Lesson Type
Skill Sharpener

Lesson Plan - Get It!

Audio:

You want to buy a new bike that costs $505 and you have $309. How much more money do you need to buy the bike?

Subtraction is used to find the difference between two numbers.

In a subtraction problem, the larger number is usually written first and the smaller number is subtracted from the larger number. In most cases, the problems are written vertically and are solved by subtracting the numbers starting in the ones place. Sometimes, the numbers on the top may include zeros and require regrouping.

As you watch Subtraction and Regrouping with Zeros 2nd Grade Math (Math & Learning Videos 4 Kids), jot down what steps are followed to subtract with zeros:

 

After the video, discuss with a parent or teacher what you remember about subtracting when the top digits are smaller than the bottom digits if a number is set up vertically.

Let’s look at the example from the beginning of the lesson.

You want to buy a new bike that costs $505 and you have $309. How much more money do you need to buy the bike?

In order to find how much more money is needed, you need to find the difference between the numbers.

  1. Align the digits by place value.
  2. Subtract the bottom number from the top number starting in the ones place. Notice how the 9 in the ones place cannot be subtracted from the 5 in the top number. Regrouping is needed in this problem.
  3. Begin regrouping in the hundreds, then move back to the tens and ones place.
  4. Since the tens place is a zero, you need to regroup from the hundreds place.
  • The 5 in the hundreds in the top number becomes a 4.
  • 5 hundreds equals 4 hundreds and 10 tens.
  • The 0 in the tens place becomes 10.
  1. Regroup again and the 10 in the tens place becomes a 9, and the 5 in the ones place becomes 15. 10 tens is equal to 9 tens and 10 ones.
  2. Now, subtract the numbers by place value. Remember the phrase “subtract down to find the difference.”

If you subtract $309 from $505, you will get $196. You need $196 more to have enough money to buy the bike.


Since addition and subtraction are opposite, or inverse, operations, you can check the answer to a subtraction problem by adding. Add the answer, or the difference, to the amount subtracted. The total should equal the starting amount:

To check the answer, add the two numbers that were subtracted. The answer we get is $505, which is the starting amount.

Discuss with a parent or teacher how you know when you need to regroup in subtraction.

Now you will practice subtracting numbers with zeros in the Got It? section as you play games and complete some interactive practice.

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