Question 209611
A water main for a street is being laid using a particular kind of pipe that
 comes in either 16-foot sections or 20-foot sections.
 The designer has determined that the water main would require 10 fewer sections
 of 20-foot pipe than if 16-foot sections were used. 
Find the total length of the water main.
:
Let n = number of 20' sections
then
(n+10) = number of 16' sections
:
20n = 16(n+10)
:
20n = 16n + 160
;
20n - 16n = 160
:
4n = 160
n = {{{160/4}}}
n = 40 ea 20'sections
:
Find the total length of the water main: 40 * 20 = 800ft
;
;
Check solution
800 = 16(40+10)
800 = 16 * 50