Question 762639
Middle person weighs twice as much as the lighter person: m = 2l -> l = m/2
Middle person weighs 30 lbs less than the heaviest: m = h - 30 -> h = m+30
The average weight = 160 = (l+m+h)/3 -> l+m+h = 480
Substitute the values for l and h above and solve for m:
m/2 + m + (m+30) = 480
5m/2 = 450
m = 900/5 = 180
So the middle person weighs 180 lb.
Check:
90 + 180 + (180+30) = 480, and the average is 160