How to do mental maths? I'm slow and retarded but want to be able to do them.
I feel like one's abstract mathematics knowledge should be supplemented by skill in mental calculations or otherwise they're just a pseud.

What are some other good and accessible resources?
I have some here. Haven't read this yet but this seems like a good starting point:
>https://en.wikipedia.org/wiki/Mental_calculation#Calculating_differences:_a_%E2%88%92_b
And that Indian lady(Shakuntala Devi)'s book (which I also haven't read yet):
>https://1lib.us/book/2852468/05b239
Are any of you faggots good at mental calculations?