In this post we will understand how we can multiply fast without any difficult calculations. Performing fast calculation can give you huge edge if you are preparing for competitive examinations like GMAT, Maths Olympiad, government entrance exams like Banking, IBPS, SSC-CGL, RBI etc
First Method (Multiples of 9)
This method work when you are provided with number which is multiple of 9 such as 99, 999, 99999 etc.
Let us study this method with the help of examples:
1. Multiply 95 * 9
a. First step is to represent number 9 in form of multiple of 10.
we are converting into multiple of 10 because calculation with number 10 is very easy
so, 95 * (10 – 1)
b. Now the number can be expanded and easily calculated
==> (95 * 10) – (95 * 1)
==> 950 – 95
==> 855
2. Multiply 84 * 99
a. First step is to represent number 99 in form of multiple of 100.
we are converting into multiple of 100 because calculation with number 100 is very easy
so, 84 * (100 – 1)
b. Now the number can be expanded and easily calculated
==> (84 * 100) – (84 * 1)
==> 8400 – 84
==> 8316
3. Multiply 112 * 999
a. First step is to represent number 999 in form of multiple of 1000.
we are converting into multiple of 1000 because calculation with number 1000 is very easy
so, 112 * (1000 – 1)
b. Now the number can be expanded and easily calculated
==> (112 * 1000) – (112 * 1)
==> 112000 – 112
==> 111,888
I hope the concept is clear for you. In case of doubt, please feel free ask in the comment section.
In the next page we will discuss the next multiplication trick.