#### Explanation:

{:($7.75),("for"),(5.2" pounds"):}rArr{:(($7.75)/(5.2)~~$1.4938),("for"),(1" pound"):} So the unit price is $1.4938 per pound.

($1.4938)/cancel("pound")xx3cancel(" pounds") =$4.47 (to the nearest cent)

Dec 16, 2016

3lb" of grapes"=$4.47 to 2 decimal places #### Explanation: $\textcolor{b l u e}{\text{Determine unit cost}}$In the context of this question unit rate is the cost of 1 (unit) pound of grapes. $\textcolor{b r o w n}{\text{Using ratio}}$$\frac{\text{cost")/("weight") ->($7.75)/(5.2)" but we need "("cost}}{1}$

To turn the 5.2 into 1 divide it by 5.2. For multiply or divide, what we do to the bottom we also do to the top to maintain correct proportions.

("cost")/("weight") ->($7.75)/(5.2) -=($7.75-:5.2)/(5.2-:5.2) = (1.4903...)/1

To reduce rounding error use $\frac{7.75 \div 5.2}{1} = \frac{7.75}{5.2}$ as unit cost.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
$\textcolor{b l u e}{\text{Determine cost of 3 pounds of grapes}}$

1 pound cost $7.75/5.2 1lb =$7.75/5.2

Multiply both sides by 3

3xx1lb=3xx$7.75/5.2 3lb=$4.47115....

3lb=\$4.47 to 2 decimal places