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5.16: Better Buy: Buying More than One

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Better Buy: Buying More than One - Reason Proportionally

As in the previous section, in Better Buys: Price for More than One, students first compute the unit price of an item at two different stores. (Note that students may use other methods.) Then they use that data to compute and compare costs of multiple items from the stores, and determine the savings. An important concept is that to determine the better buy, either the number of items must be the same so that the prices can be compared or the prices must be the same so that the number of items can be compared. This latter concept should be highlighted throughout the grades.

1. $2 less at Morsel’s Market

$6 for 2 gallons of milk at Morsel’s Market (Unit price is $3/gallon)

$8 for 2 gallons of milk at Flynn’s Foods (Unit price is $4/gallon)

2. $3 less at Flynn’s Foods

$15 for 3 bottles of orange juice at Flynn’s Foods (Unit price is $5/bottle)

$18 for 3 bottles of orange juice at Morsel’s Market (Unit price is $6/bottle)

3. $8 less at Flynn’s Foods

$8 for 4 ice cream bars at Flynn’s Foods (Unit price is $2/ice cream bar)

$16 for 4 ice cream bars at Morsel’s Market (Unit price is $4/ice cream bar)

4. $5 less at Flynn’s Foods

$10 for 5 boxes of crackers at Flynn’s Foods (Unit price is $2/box)

$15 for 5 boxes of crackers at Morsel’s Market (Unit price is $3/box)

5. $8 less at Morsel’s Market

$24 for 4 bags of oranges at Morsel’s Market (Unit price is $6/bag)

$32 for 4 bags of oranges at Flynn’s Foods (Unit price is $8/bag)

6. $7 less at Morsel’s Market

$42 for 7 watermelons at Morsel’s Market (Unit price is $6/watermelon)

$49 for 7 watermelons at Flynn’s Food (Unit price is $7/watermelon)

Which store has the better buy?

How much less are 2 boxes of cereal at that store?

& \mathbf{Describe} && \text{I see signs for boxes of cereal at two stores.}\\ &&& \text{Borson's Foods} : \ 4 \ \text{boxes for} \ \$12\\&&& \text{Saferoad Market} : \ 5 \ \text{boxes for} \ \$20\\ & \mathbf{My \ Job} && \text{Figure out which store has the better price for two boxes of cereal.}\\&&& \text{Then compare prices to find out how much less.}\\& \mathbf{Plan} && \text{I'll figure out the price of one box at each store. Then I can find the price for two}\\&&&\text{boxes and compare the total prices.} \\& \mathbf{Solve} && \text{Borson's Foods} : \ 4 \ \text{boxes for} \ \$12 \ \text{is} \ 12 \div 4, \ \text{or} \ \$3 \ \text{for one box and} \ \$6 \ \text{for} \ 2 \ \text{boxes.}\\&&& \text{Saferoad Market} : \ 5 \ \text{boxes for} \ \$20 \ \text{is} \ 20 \div 5, \ \text{or} \ \$4 \ \text{for one box and} \ \$8 \ \text{for} \ 2 \ \text{boxes.}\\&&& \$8 - \$6 = \$2. \ \text{I will save} \ \$2 \ \text{by buying cereal at Borson's Foods.}\\& \mathbf{Check} && \text{Borson's Foods} : \ \$12 \div 4 = \$3 \ \text{and} \ 2 \times \$3 = \$6\\&&& \text{Saferoad Market} : \ \$20 \div 5 = \$4 \ \text{and} \ 2 \times \$4 = \$8\\&&& \$8 - \$6 = \$2

Which store has the better buy?

How much less are 2 gallons of milk at that store?

Which store has the better buy?

How much less are 3 bottles of orange juice at that store?

Which store has the better buy?

How much less are 4 ice cream bars at that store?

Which store has the better buy?

How much less are 5 boxes of crackers at that store?

Which store has the better buy?

How much less are 4 bags of oranges at that store?

Which store has the better buy?

How much less are 7 watermelons at that store?

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