Credit card.Even if you found a lender to do it, flat closing costs would be a ridiculous % of loan amount.A flat $1500 origination fee is mathematically identical to 30 points upfront on a $5k loan.

This may get them votes, but unless mathematics work differently there, it will have an adverse effect on the  economy

I will leave it to others to dig further into the mathematics of it all, but those are some initial things to consider.

So that's when I started to wonder, because even if you are paying all cash, its still not a good return from a mathematical standpoint.

Another no I got when I was quite young was around mathematics.

One doesn't have to have a science degree with years of advanced mathematics, or an economics hobby, or more than an 8th grade education. 

If you have modest retirement savings, and are in your highest earning years - taking the tax deduction today is going to work out the best mathematically - you can take the money off the top today when your income is high, and pull the money out later at near-zero tax rates when you are trying to live off a too-small 401k.If you are young and in a low tax bracket, the Roth is golden, you are missing out on a known small tax savings for the long term benefit of not having to worry about income tax policy.

Mathematically, it doesn't matter if you have this done with one loan that you held for 365 straight days, or 2-3x on shorter-duration loans as you outlined above.To make that more intuitive, even if you reinvest 3x a year... each of those investment periods will only be for less than a full year, right?

I even disagree with my friend @Ned Carey, which is the first time that happened...In mathematical terms, I would tell you to underwrite to IRR.

Does anyone have any recommendations on books, blogs, or any other resources that can help with truly understanding the financing/mathematics behinds deals?