decrease — Definition, Formula & Examples
Decrease means to become smaller in value or amount. When a number decreases, it goes down.
A decrease occurs when a quantity changes to a lesser value. The amount of decrease is the difference found by subtracting the new, smaller value from the original value.
Key Formula
Where:
- = The starting number before it went down
- = The ending number after it went down
Worked Example
Problem: A jar had 15 marbles. You gave away some, and now there are 9 marbles. By how much did the number of marbles decrease?
Step 1: Subtract the new amount from the original amount.
Answer: The number of marbles decreased by 6.
Why It Matters
You use decreases whenever you track things going down — temperature dropping, money being spent, or a score falling. Recognizing a decrease helps you set up the correct subtraction problem in word problems.
Common Mistakes
Mistake: Subtracting in the wrong order and getting a negative number.
Correction: Always subtract the smaller new value from the larger original value. If the temperature went from 80° to 65°, compute 80 − 65, not 65 − 80.