A quick tip on how to calculate tips:<p>Finding 10% of an amount is easy.  All you have to do is move the decimal point over one position to the left.  For example if you had an $80 dinner, then 10% of that is $8.  Just double that amount to find the 20% tip, in this case $16.<p>I think that with a little thought most people should be able to figure out these tricks, but you are right, most people don't bother and their skills fade.