What is the difference in price per ounce?

A 30-oz box of cornflakes costs $1.79 and a 3-lb box costs $1.87. To the nearest tenth of a cent, what is the difference per ounce?

1 Answer
Apr 12, 2018

#2.1# cents per ounce to the nearest #10^("th")#

Explanation:

Note that we are instructed 'to the nearest 10th'. This means we need to work in decimals and not fractions.

Fractions would give an exact answer.

Using ratio but in fraction format (this is NOT A FRACTION)

#color(brown)("Consider condition 1: "color(white)("ddd")30" oz at "$1.79)#

Write as: #("cost in cents")/("wieght in oz") ->179/30->(179-:30)/(30-:30) = color(green)((5.966bar6)/1)#
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

#color(brown)("Consider condition 2: "color(white)("ddd")3" lb at "$1.87)#

Firstly we need to convert the pounds into ounces. We know that there are 16 ounces in every 1 pound. So as there are 3 pounds we have 3 lots of 16 ounces:

#("cost in cents")/("wieght in oz") ->187/(3xx16) = 187/48=(187-:48)/(48-:48)=color(green)((3.895833bar3)/1)#
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
#color(brown)("Determine the difference")#

#5.966666..#
#ul(3.895833... larr" Subtract")#
#2.070833....#

#2. color(white)("d")0color(white)("d")color(red)(||)color(white)("d")7color(white)("d")0color(white)("d")8color(white)("d")3color(white)("d")3....#
#color(white)("dddd")color(red)(uarr)#

#color(red)("Cut off point")#

The digit to the right of the cut off point (7) satisfies 'more than or equal to 5' so we increase the digit to the left of the cut of point (0) by 1 giving:

#2.1# cents per ounce to the nearest #10^("th")#