so, this should help you realize how low the chance of a runner runner straight happening are.

there are 8 cards that could come that would give you then 8 outs on the river, and 8 cards that could come that would give you 4 outs on the river.

8/47 on the turn * 8/46 on the river = 2.9%
8/47 on the turn * 4/46 on the river = 1.5%

So the odds of a backdoor straight like this coming through is 4.4%.

This is actually higher than i read on a website, I read you have a 1 in 38 chance, or 2.6%, where'd I go wrong?