This rule is true for marbles, but in other situations, you can subtract a big number from a small one. For example, if you have $4 and you buy something that costs $6, you end up with less than $0 dollars — that is, –$2, which means a debt of $2.
A number with a minus sign in front of it, like –2, is called a negative number. You call the number –2 either negative two or minus two. Negative numbers appear on the number line to the left of 0.
Subtracting a large number from a small number makes sense on the number line. Just use the rule for subtraction: Start at the first number and count left the second number of places.
When you don't have a number line to work with, here's a simple rule for subtracting a small number minus a big number: Switch the two numbers around and take the big number minus the small one; then attach a negative sign to the result.
Sample questions
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Use the number line to subtract 5 – 8.
–3. On the number line, 5 – 8 means start at 5, left 8.
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What is 11 – 19?
–8. Because 11 is less than 19, subtract 19 – 11, which equals 8, and attach a minus sign to the result. Therefore, 11 – 19 = –8.
Practice questions
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Using the number line, subtract the following numbers:
a. 1 – 4 = ________________
b. 3 – 7 = ________________
c. 6 – 8 = ________________
d. 7 – 14 = ________________
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Find the answers to the following subtraction problems:
a. 15 – 22 = ________________
b. 27 – 41 = ________________
c. 89 – 133 = ________________
d. 1,000 – 1,234 = ________________
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Subtraction problems with number line
a. 1 – 4 = –3. Start at 1, down 4.
b. 3 – 7 = –4. Start at 3, down 7.
c. 6 – 8 = –2. Start at 6, down 8.
d. 7 – 14 = –7. Start at 7, down 14.
Subtraction problems
a. 15 – 22 = –7. Fifteen is less than 22, so subtract 22 – 15 = 7 and attach a minus sign to the result: –7.
b. 27 – 41 = –14. Twenty-seven is less than 41, so subtract 41 – 27 = 14 and attach a minus sign to the result: –14.
c. 89 – 133 = –44. Eighty-nine is less than 133, so subtract 133 – 89 = 44 and attach a minus sign to the result: –44.
d. 1,000 – 1,234 = –234. One thousand is less than 1,234, so subtract 1,234 – 1,000 = 234 and attach a minus sign to the result: –234.