# 4.13: Write Equations Extras

**At Grade**Created by: CK-12

**Better Buy: Unit Price - Proportional Reasoning**

In **Better Buy: Unit Price**, two signs showing prices for multiple items of the same type at two stores are displayed. Students reason proportionally to first determine the price for one toy (unit price) at each store. Then they compare prices to identify the better buy, that is the item of lesser price. To determine unit price, students divide. All division computations in this section involve basic facts.

**Solutions**

- Jim’s Sports; \begin{align*}\$20 \div 4\end{align*} or $5 for one paddle and ball (\begin{align*}\$18 \div 3\end{align*}, or $6 at A-One Athlete).
- A-One Athlete; \begin{align*}\$10 \div 5\end{align*}, or $2 for one Frisbee (\begin{align*}\$6 \div 2\end{align*}, or $3 at Jim’s Sports).
- Jim’s Sports; \begin{align*}\$36 \div 6\end{align*}, or $6 for one badminton racquet (\begin{align*}\$28 \div 4\end{align*}, or $7 at A-One Athlete).
- A-One Athlete; \begin{align*}\$30 \div 10\end{align*}, or $3 for one golf ball (\begin{align*}\$24 \div 6\end{align*}, or $4 at Jim’s Sports).
- A-One Athlete; \begin{align*}\$18 \div 9\end{align*}, or $2 for one birdie (\begin{align*}\$12 \div 4\end{align*}, or $3 at Jim’s Sports).
- Jim’s Sports; \begin{align*}\$15 \div 3\end{align*}, or $5 for one can of tennis balls (\begin{align*}\$30 \div 5\end{align*} or $6 at A-One Athlete).

**Which store has the better buy for one yo-yo?**

\begin{align*}& \mathbf{Describe} && \text{I see signs for yo-yos at two stores.}\\ &&& \text{Terry’s Toys} : \ 3 \ \text{yo-yos for} \ \$12\\ &&& \text{Geena’s Gifts} : \ 5 \ \text{yo-yos for} \ \$15\\ & \mathbf{My \ Job} && \text{Decide which store has the better buy for one yo-yo.}\\ &&& \text{Better buy means it costs less.}\\ & \mathbf{Plan} && \text{I’ll figure out the price for one yo-yo at each store.} \\ &&& \text{Then I will compare the prices.}\\ & \mathbf{Solve} && \text{Terry’s Toys}: \ \$12 \div 3 = \$4 \ \text{for one yo-yo}\\ &&& \text{Geena’s Gifts}: \ \$15 \div 5 = \$3 \ \text{for one yo-yo}\\ &&& \text{Geena’s Gifts has the better buy}\\ & \mathbf{Check} && \$3 < \$4 \ \text{so one yo-yo costs less at Geena’s.}\end{align*}

**Which store has the better buy for one paddle and ball?**

**How much is the paddle and ball at that store?**

**Which store has the better buy for one Frisbee?**

**How much is one Frisbee at that store?**

**Which store has the better buy for one racquet?**

**How much is one racquet at that store?**

**Which store has the better buy for one golf ball?**

**How much is one golf ball at the store?**

**Which store has the better buy for one birdie?**

**How much is one birdie at the store?**

**Which store has the better buy for one can of tennis balls?**

**How much is one can at that store?**

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