Question

The total cost of an item including sales tax is directly proportional to its price. If the total cost of a $25 item is $25.75, what is the total cost on a $60 item?

Answer 1

$\bf \qquad \qquad \textit{direct proportional variation}\\\\ \textit{\underline{y} varies directly with \underline{x}}\qquad \qquad y=kx\impliedby \begin{array}{llll} k=constant\ of\\ \qquad variation \end{array}\\\\ -------------------------------$

$\bf \textit{cost(c) is directly proportional to price(p)}\qquad c=kp \\\\\\ \textit{we also know that } \begin{cases} p=25\\ c=25.75 \end{cases}\implies 25.75=k25\implies \cfrac{25.75}{25}=k \\\\\\ 1.03=k\qquad thus\qquad \boxed{c=1.03p}\\\\ -------------------------------\\\\ \textit{what's \underline{c} when \underline{p} is 60?}\qquad c=1.03(60)$