Product of Numbers close to 100:

Lets take you have to multiply 91 and 95 . First take their difference from 100. ie 100-91=9and 100-95=5 . Now reduce this difference from the other number .ie 91-5 or 95-9 ==86 . This is the first 2 digits of the result . Now for the last 2 digits just multiply the differences ,ie, 9*5=45.

So the result is  91*95=8645.