Question

Kyle is shopping for his favorite

cereal at the grocery store. The
9 ounce box costs $2.52 while the 12 ounce box costs $3.60. Which is the better deal? How much will he save per ounce?

A) 9 oz.; 20¢/oz.
B) 12 oz.; 20%/oz.
C) 9 oz.; 2¢/oz.
D) 12 oz.; 2¢/oz.
E) 12 oz.; 9¢/oz.

Answer 1

better deal for Kyle means which is cheaper, namely which one gives the more Cereal per penny.

well, we can look at both deals from a standpoint of a rate, let's see how much each one costs per ounce.

`\begin{array}{ccll} oz&\$\\ \cline{1-2} 9 & 2.52\\ 1& x \end{array} \implies \cfrac{9}{1}~~=~~\cfrac{2.52}{x}\implies 9x=2.52\implies \underset{\textit{\LARGE better deal}}{\stackrel{\textit{28 cents per ounce}}{x=\cfrac{2.52}{9}\implies x=0.28}} \\\\[-0.35em] ~\dotfill\\\\ \begin{array}{ccll} oz&\$\\ \cline{1-2} 12 & 3.60\\ 1& y \end{array} \implies \cfrac{12}{1}~~=~~\cfrac{3.60}{y}\implies 12y=3.6\implies \stackrel{\textit{30 cents per ounce}}{y=\cfrac{3.6}{12}\implies y=0.30}`

well, yes, "x" is better but by how much? well, 0.30 - 0.28 = 0.02, by 2¢ at Mt Rushmore.