Add and Subtract Decimals

When you add or subtract decimals, you have to line up the decimal points. Once the decimal points are lined up, then add or subtract.

Examples:

1). 7.2 + 9.5

First line up the decimals:

2). Camia has a checking account balance of $245.30. What is Camia's new balance after writing a check for $24.95?

**First, we have to determine if we need to add or subtract. Notice that Camia wrote a check for $24.95 and thus she made a payment for something. We have to subtract this payment from her current balance.**

**Second, we must line up the decimals with the larger decimal on top and then we can subtract as we would with whole numbers:**

**Cashier and Customer Crunch Time**

**You can set your students up in groups of two. To begin, assign one student as a cashier and one student as the customer. They can switch roles after 10 minutes. Give your students a list of grocery items they can choose from with prices, fake money and coins. The student has to choose two items from the list and give the correct money to the cashier. The cashier has to recount the money to make sure it is correct. The student with the most correct answers wins a homework pass. **

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Created by Wanda Collins May 10, 2015 at 1:56pm. Last updated by Wanda Collins May 10, 2015.

Question: Why is this a mathematical limerick?

( (12 + 144 + 20 + 3 Sqrt[4]) / 7 ) + 5*11 = 9^{2} + 0 .

Answer:

A dozen, a gross, and a score,

plus three times the square root of four, divided by seven, plus five times eleven, is nine squared and not a bit more.

---Jon Saxton (math textbook author)

**Presentation Suggestions:**

Challenge students to invent their own math limerick!

**The Math Behind the Fact:**

It is fun to mix mathematics with poetry.

**Resources:**

Su, Francis E., et al. "Math Limerick." Math Fun Facts.

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