In Multiplying Numbers that are Close to base 100 (part-1), we saw how to multiply numbers that are below or above base 100 in just one line. Here in part-2, we will see how to multiply numbers ‘Vertically and Cross-wise’ where one number is above the base and the other is below.

For multiplying such numbers:
  1. Subtract (from the number which is above the base 100) or add (with the number which is below the base 100) crosswise to find the first 2 or 3 digits and append ‘00’ to the right.
  2. Then subtract the product of both the differences from the base 100 from this result.
Suppose you want to multiply 102 by 97

102 is 2 more than 100 and 97 is 3 less than 100.
So, subtract (102-3) or add (97+2) crosswise to get 99.
Append 2 zeros to 99 to get 9900.
Now, subtract the product of both the differences that is 6 (2x3=6) from 9900.
You get 9900-6 = 9894

So, 102 x 97 = 9894

Another example,

107 x 98 =?

107 is 7 more than 100 and 98 is 2 below 100.
So, subtract (107-2) or add (98+7) crosswise to get 105.
Append 2 zeros to 105 to get 10500.
Now, subtract the product of both the differences (7x2=) 14 from 10500.
You get 10500-14 = 10486
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