What is 13% of 91?
I don't know. Do you?
But I now 10% of 91 is 9.1
I got somewhere eh?
Hey also I know that 1% of 91 is 0.91 Duh! lets triple that.
0.91 x 3 = 0.9x3 + 0.01x3 = 2.7 + 0.03 = 2.73
Now lets add 9.1..
11.83 Weee!
(Now my date is rolling her eyes and the waiter is stone faced)