Think of subtraction as removing parts from a whole. Consider the following word problem.

In the problem below, Sebastian has 8 pencils and he gives away 5 pencils to his friends.

Sebastian is experiencing a loss of 5 pencils, so the subtraction problem to solve to get the answer is 8 - 5 and 8 - 5 = 3.

Sebastian is left with 3 pencils.

Peter has 20 dollars in his pocket. He buys a 32 ounces vanilla ice cream for 8 dollars from the best ice cream shop in the neighborhood. How much is Peter's change?

In this situation, Peter is also experiencing a loss because some money will be taken away from him for the ice cream.

Therefore, we need to do this subtraction to get the answer: 20 - 8. This subtraction requires regrouping since you cannot remove eight from zero.

Peter's change = 20 - 8 = 12 dollars.

Suppose that a car dealer has an inventory of 15,258 Honda Accord they have to sell by the end of 2008. Suppose they don't meet their goals and sell only 12456 Honda Accord by the end of 2008. How many cars are left in the backyard of the car dealer?

In this situation, we are removing parts from a whole to get the leftover.

Therefore, we need to do this subtraction to get the answer: 15258 - 12456. This subtraction also requires regrouping since you cannot remove four hundreds from two hundreds.

Number of cars in the back yard = 15258 - 12456 = 2802

At a local supermarket, a box of cereal usually costs 5.56 dollars. This week, the supermarket sells the box of cereal for 3.42 dollars. How much money will you save if you buy this cereal at this supermarket?

Once again, in this situation, there is a decrease in the price.

Therefore, we need to do this subtraction in order to get the answer: 5.56 - 3.42. This is a straightforward subtraction with no regrouping!

Saving = 5.56 - 3.42 = 2.14 dollars

**Problem #4**

A stock bottle of medication contains 500 mg of a drug. You used 125 mg for one prescription and 62.5 mg for a second prescription, while the third prescription was for a child and only 25.25 mg were necessary.

A. What quantity (mg) of the medication has been used? Round to the nearest hundredths.

B. What quantity (mg) of the original medication is left in the stock bottle? Round to the nearest tenths.

**Solution**

A. We can find the quantity that has been used by adding 125 mg, 62.5 mg, and 25.25 mg together.

125 mg + 62.5 + 25.25 = 212.75 mg

212.75 rounded to the nearest hundredths is 212.75

B. We can find the quantity that is left in the stock bottle by subtracting 212.75 mg from 500 mg.

500 - 212.75 = 287.25

287.25 rounded to the nearest tenths is 287.3

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