I need to say that Vedic math is not without controversy as the name is a misnomer (ie not from the Vedic period but from a 1965 book on the subject) and its more a collection of arithmetic tricks and not math perse.
As a kid, when I was asked to do this kind of calculation by a friend, I'd ask him why he needed the answer and while he was responding, work it out mentally and then answer. It gave me a few moments but people thought my answer came out instantaneously which was okay by me.
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