Complicated Percentage Formula?

Alright, I'm completely stuck here.

I'm looking to create a formula to find a minimum 20% increase in a set of DJI data over time. I have the data laid out so that the date is in column A, closing price is in column B, and percentage change from the day before in column C.

I need to know every pair of dates that yield this 20% increase, keeping in mind that after a set of dates has been used it cannot be used again. (As an example, say January 12th 1982 to March 3rd 1983 had a 20% increase. I wouldn't want to know that August 14th 1982 to June 22nd 1983 also had that increase.)

Anyone have a clue how to do this? I know it'll be extremely complicated so any help is much appreciated.