User blog comment:Oioiaussie/Buy playgrounds? A common misconception!/@comment-5110407-20120531221819/@comment-5039776-20120601021218

It's the same math:

Cost differential (1Ge vs 9 VFTs): 189,000 - 90,000 = 89,000

Revenue differential:

- 1 GE gives 750 every 2 hours, so assume 9 cycles per day = 6,750 coins per day

- 9 VFTs gives 200 x 9 every 8 hours, so assume 3 cycles per day = 5,400 coins per day (200 x 9 x 3)

- So, revenue difference is 1,350 coins per day in favour of the GE.

Time to get the cost difference back = 89,000 / 1,350 = 66 days.

Hope this helps.