Consider the following questions:
- What’s the difference in distance between taking the Eighth Street Bridge versus MLK Boulevard?
- How much more money do we need to save?
- If we take away 45 of the plants for the front garden, how many will be left for the back garden?
- If all vacation prices have been decreased (or reduced ) by $20, how much is this one?
All these questions involve the process of subtraction to find the answer—a process that you often meet when dealing with money. You can see that the “trigger” words for subtraction are again in bold.
One way you can think of subtraction is as the process that undoes addition. For example, instead of saying “$10 minus $7.85 leaves what?” you could say, “What would I have to add to $7.85 to get to $10?”
Adding on 5 cents gives $7.90, another 10 cents gives $8, and another $2 will give you a total of $10. So, the total amount to add on is . This is the same answer as the one obtained by subtraction: .
In other words, you can always check or work out a subtraction problem by using addition. For example, if you calculate 1874 – 1476 = 398, then a quick check is to make sure , which it does.
Working out calculations like this on an everyday basis may help you to feel more confident in working with numbers. You can always check your answer on a calculator, if you like.