the distance between two cities is 390 mi on a map the distance is represented by 15 in in the same map Rockville and Sullivan are 21 in apart . What is the actual distance between these two cities?

Question

the distance between two cities is 390 mi  on a map the distance is represented by 15 in  in the same map Rockville and Sullivan are 21 in apart . What is the actual distance between these two cities?

jdoe0001 · Answer

$\bf \begin{array}{llll}
\textit{distance in miles}&\textit{map in inches}\
390&15\
x&21
\end{array}\implies \cfrac{390}{x}=\cfrac{15}{21}
$

anonymous · Answer

you cross multiply, i assume? 
so whenever you see a problem that's set up like this the best thing to think of is an 'x' between the two equations so you have 390 touches 21 and 15 touches x, so you know that you have to do something with 390 and 21 to figure out how 15 is related to x. 

So multiply 390 by 21 which gives you 8,190
then you take the product of that and divide it by 15 which gives you 546 and that is you answer for 'x'.

Basically what you are doing is figuring out the ratio. When you have to measurements that are parallel in some way (so the ratio of the map is similar to the ratio of the actual distance between the two cities) then you can use the second ratio to figure out any missing component with the first. I hope this wasn't more confusing. let me know if you have any questions.

anonymous · Answer

Thank you so much hanifah, it was giving me a headache.

anonymous · Answer

No problem :)