It depends on a person weather he/she can do it easily or not... But as we've know, there are some shortcuts that we can apply that involves multiplication.
First, memorize a 1 to 10 multiplication table... Through this, you can multiply a certain equation easily.
If you could encounter this kind of equation; 11×5
You must put five on the ones and tens digit, so you'll have; 55 as the answer
If you had a trouble memorizing the multiplication of 9, than here's the secret...
09 or 9
Notice that the ones and the tens digit pattern.... In the ones digit, it keeps adding 1 while in the tens digit, it keeps decreasing 1...
Hope it Helps =)