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)