I'll be honest. I'm terrible at mental math. It's definitely my biggest weakness. I've always been bad at it, so I relied upon calculators throughout school, but that only led me to never develop the skill. Now I do fine on my quantitative exams on school because I have a calculator, but the moment I get a mental math question in interviews, my stomach drops and I really struggle.
I know I need to improve this ability for interviews. As much as I disagree with it, people seem to take mental math skills as a proxy for intelligence. Anybody have any suggestions on how to build my mental math ability from the ground up? I'm pretty much starting at square one here. Any resources, books, or study plans would be really helpful. Thanks in advance.
Don't add 17. Add 20, then subtract 3.