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Compare situations using unit rates

A unit rate describes the amount of one quantity corresponding to one unit of another, found by dividing the quantities and labeling the resulting rate appropriately. Comparisons require expressing situations in compatible units, including rates involving fractions and decimals, and interpreting which rate is greater rather than comparing total amounts or denominators alone; this reasoning supports proportional relationships represented in tables, graphs, and equations.

Detailed Explanation: Compare situations using unit rates

A unit rate tells how much of one quantity corresponds to exactly 11 unit of another quantity. To compare two situations, find both unit rates using the same units.

Example:
Store A sells 34\frac{3}{4} pound of grapes for 5.25.StoreBsells. Store B sells (1.2)poundsofgrapesforpounds of grapes for$7.80$. Which store has the lower price per pound?

Step 1: Identify the units to compare.
We will compare the cost for 11 pound, so each unit rate should be in dollars per pound.

Step 2: Find Store A’s unit rate.

$5.2534 lb\frac{\$5.25}{\frac{3}{4}\text{ lb}}

Convert 34\frac{3}{4} to a decimal:

34=0.75\frac{3}{4}=0.75

Now divide:

5.25÷0.75=75.25\div 0.75=7

Store A’s unit rate is 7.00$ per pound.

Step 3: Find Store B’s unit rate.

$7.801.2 lb=7.80÷1.2=6.50\frac{\$7.80}{1.2\text{ lb}}=7.80\div 1.2=6.50

Store B’s unit rate is 6.50$ per pound.

Step 4: Compare the unit rates.

$6.50<$7.00\$6.50<\$7.00

Store B has the lower price per pound, so Store B is the better buy.

Remember: Compare the unit rates, not the total prices or the amounts of grapes.

Learn by doing: Compare situations using unit rates

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Ratios - Unit Rates, Find Best Price - Fractions


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