Individual build rates are:
George: 1 house per year
Greg: 1/2 " " "
Gabriel: 1/3 " " "
Glen: 1/4 " " "
Gordy: 1/5 " " "
If all 5 people work together, then you add together their individual build rates.
Group rate = 1 + 1/2 + 1/3 + 1/4 + 1/5 = 137/60 houses per year.
5 people build 137/60 houses per year,
Therefore, time to build one house is 60/137 years = 0.43796 yrs
Combined build time = 5 months, 7.7 days
Time required = 5mths, 8 days