Subtracting Through Twenty

Now that we have single-digits out of the way, let's look at some numbers between one (1) and twenty (20). If you were comfortable adding single-digit numbers, these subtraction problems will be easy.

We've been saying that subtraction problems are the opposite of addition problems. If you look at the equations written out you will see a pattern.
4 + 5 = 9 can also be written 9 = 5 + 4
9 - 5 = 4 (see the similarities?)

If you get stuck you can always ask your self "what number plus this number will give me the bigger answer?" Like this...
Question: 15 - 7 = ?
(1) If you don't have the answer memorized, ask yourself "What number plus seven (7) is equal to fifteen (15)?"
(2) You will remember that 7 + 8 = 15
(3) If 7 + 8 = 15, then 15 - 7= 8

Try that idea with these examples.

Examples:
15 - 7 = ? (remember that 7 + 8 =15)
18 - 9 = ? (remember that 9 + 9 = 18)
12 - 8 = ? (remember that 8 + 4 = 12)

Column by Column

You already know that subtraction problems need a minus (-) sign. They can also be written in two ways. On our pages you will see the problem in a left-to-right format. For simple numbers, this layout works fine. As you start to use larger numbers you will see subtraction problems in a vertical (up and down) format. You will move through the problem in the same way you did with addition. You will break the problem up into several smaller subtraction problems. You will start with the column of numbers on the right. Once you finish with the ones column you will move to the tens, hundreds, and any other columns of numbers that you have. Just take simple steps.

Empty Space

When you use that up and down layout, you will find numbers that don't match. If you have the problem 15,687 - 5, there are whole columns of numbers with no value that have no values. Just treat those empty spaces like zeros (0). Like this… 15,687 - 5 = ? 7 - 5 = 2 8 - 0 = 8 6 - 0 = 6 5 - 0 = 5 1 - 0 = 1 So 15,687 - 5 = 15,682

RELATED ACTIVITIES

Comparing One and Two-Digit Differences (No Borrowing)
- Play Activity

Single-Digit Subtraction Quiz
- Play Activity

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