All that debt sounds good mathematically, but in times like this does it still sound as good?

@Shafi NossWithout an example, I can't be sure we're on the same page.Say you bought a property for $200k 10 years ago, depreciated $50k of it, and are selling it for $300k now.You have a $150k capital gain, $50k of which is taxed under 1250 recapture rules, and $100k under long-term cap gains rules.Now, a mathematically flawed example below, just to illustrate the concept.

While, it will take longer to close mortgages, mathematically I believe it will save interest expense. 

If you decide to refi and are mathematically able to factor in those costs to your sale, (i.e. is it plausible you will be able to add an additional $3890 to your list price in 15 months and successfully sell your home?) 

The thing about ML is that it's just mathematical modeling that uses a fairly simple optimization technique.

I think mathematically it makes sense assuming you can get a better return over the next 20 years than it will get if you move it back into the market. 

It's a mathematical equation, that's it.

Refi from 8% to 3% or 5% to 3% you will have the same closing costs +-.It's a mathematical equation on your tolerance as an investor and if this transaction is in line with your short and long term goals.

This is a mathematical (with $ in the formulas) decision. 

But the math moves you a long way towards coming up with informed decisions.The same sorts of mathematical analysis can help you determine whether to buy house #1 for $200k, or house #2 for $250k.