Question

Anita sees in her nutrition book that a 7.5-ounce piece of cake has 900 calories. how many calories will she save if she takes only a 2.5 ounce piece?

Answer 1

$\bf \begin{array}{ccll} \stackrel{cake}{oz}&calories\\ \text{\textemdash\textemdash\textemdash}&\text{\textemdash\textemdash\textemdash}\\ 7.5&900\\ 2.5&x \end{array}\implies \cfrac{7.5}{2.5}=\cfrac{900}{x}\implies x=\cfrac{2.5\cdot 900}{7.5}$

so, the 2.5oz cake will be "x" calories, pheeew, she'll be taking in 900 - x less calories.