Multiplication Shotcuts 2

Multiplication of two digit numbers


Multiplying two digit numbers using column method or by using calculator shall not work for competitive exams. For the former, you will not have time and for the latter, you will not have a calculator in hand :p. So let us see some shortcuts to multiply two digit numbers.

After practicing these methods you will never need a pen to do the math. Victoryyy!!!!

1. By splitting up of number according to our convenience
  

    Method 1 : Multiplication using multiples.

    Example 1 : 17 * 18
  
    Here you can split 18 as 6 * 3. Now our question becomes 17 * 6 * 3

    Multiplication with a single digit is far easier. 
  
    17 * 6 = 102
    102 * 3 = 306

   Method 2 : Multiplication using distribution 

    Example 2 : 17 * 15

    In this method we will split 15 as 10 + 5 . Multiplying some number with 10 ad 5 is                        pretty easy compared to ther numbers.

   17 * 15 = 17 * 10 + 17 * 5
     
   17 * 10 = 170
   17 * 5 = 85
   
   170 + 85 = 255.

2. Multiplication by 15 (For even numbers).

   We saw in the previous example that when multiplying with 15 what you do is you are basically           multiplying the given number with 10 and 5 and then adding them both, There is an easier way to
   do the same.

   1. Take half of the number.
   2. Add it to the number itself.
   3. Multiply with 10 ( or perhaps, put a zero at the end ).

   Example 3: 48 * 15
   
   1. 48/2 = 24.
   2. 48 + 24 = 72.
   3. 72 * 10 = 720.

   i.e 48 * 15 = 720.