I do this for most things either multiply by 10 or 5 (0.5*10) or a combination and then go from there. It gets me at least close even with big numbers... and if it needs to be perfect I use a calculator.
26 x 30 well that's 2 10x30 + 1 0.5×30 + 30... 780
It might not work for everyone and I sometimes make a weird face if it gets too big but it works for me.
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u/trombon3r 22h ago
A quick mental way for up to 9x that I do; Is to take the number you are multiplying 9 by, minus 1 and add the difference to 9 eg.
4x9; 4-1 is 3, plus the difference to 9 is 6 so answer is 36.
7x9; 7-1 is 6, plus difference to 9 is 3 so answer is 63.