Question 750403
The electrical resistance of a wire varies directly as its length and inversely
 as the square of its diameter. 
A wire with a length of 200 inches and a diameter of one-quarter of an inch has
 a resistance of 20 ohms. 
Find the electrical resistance in a 500 inch wire with the same diameter.
:
let r = the resistance of a 500" wire
Since resistance varies directly with length and the diameter is the same we can:
{{{r/20}}} = {{{500/200}}}
Cross multiply
200r = 20*500
Divide thru by 20
10r = 500
r = 500/10
r = 50 ohms