kinda mathy.
to figure out using compound interest how long it will take your money to double, divide the percent interest your getting by 72.
so
8% interest will take 9 years to double.
ahh the joys of compound interest.
the other thing I do, I don't know how much of a trick it is, and how useful it would be to most people is in multiplying large numbers.
45X182
I'd do 40X100 to give 4000
then 5 X10 to give 4500
40X80 to give 7700
5X80 for 8100
40x2 for 8180
5X2 fo 8190
works really well for estimating. you also have to be able to keep multiple numbers in your head. often I don't bothing thing 40X100=4000 I'd tjust think 4and then keep adding numbers to it based on if theyd go before or after. but thats alot harder to explain
