Or do it like we did with slide rules: logarithms
3x5 = 10^(log(3)+log(5)) = 10^(log(3.5)+1) = 35
(log is the logarithm, base 10)
Of course, you would then have to memorize the log table or have one in front of you.
Of course, you would then have to memorize the log table or have one in front of you.
They have calculators now the size of postage stamps that have logs base n so no tables needed ;(