Question

Stefan sells Jin a bicycle for ​$136 and a helmet for ​$18. The total cost for Jin is ​140% of what Stefan spent originally to buy the bike and helmet. How much did Stefan spend​ originally? How much money did he make by selling the bicycle and helmet to​ Jin?

Answer 1

well, what Stefan paid originally was really "x", which oddly enough is the 100%.

now Stefan is selling the bike and helmet for 136 + 18 = 154 bucks to Jin, and we also know that's 140% of "x", so what the heck is "x"?

`\begin{array}{ccll} amoubnt&\%\\ \cline{1-2} x & 100\\ 154& 140 \end{array} \implies \cfrac{x}{154}~~=~~\cfrac{100}{140} \\\\\\ \cfrac{ x }{ 154 } ~~=~~ \cfrac{ 5 }{ 7 }\implies 7x=770\implies x=\cfrac{770}{7}\implies x=110`