Question 30014
Gary hung seven strings of holiday lights on his house.
x =  # strings with 75 lights
7 - x = # strings with 100 lights
75x + 100(7 - x) = 400 + (75x + 100(7-x))/3
3(75x + 100(7-x)) = 1200 + 75x + 100(7 - x)
225x + 300(7 - x) = 1200 + 75x + 100(7 - x)
225x + 200(7 - x) = 1200 + 75x
150x + 1400 -200x = 1200 
-50x + 1400 = 1200 
-50x = -200
x = 4
7 - x = 3
There are 4 strings with 75 lights and 3 strings with 100 lights
check
75*4 + 100(7 - 4) = 400 + (75*4 + 100(7-4))/3
300 + 300 = 400 + (300 + 300)/3
600 = 400 + 200
600 = 600
OK