Total area of the 64 small squares of aches board is 400cm2. There is 3cm wide border around the chess board. What is the length of each side of the chess board?

A. 1
B. 2
C. 3
D. 4

Explanation:
Let the numbers be 13a and 13b.
Then, 13a * 13b = 2028 => ab = 12.
Now, co-primes with product 12 are (1, 12) and (3, 4).
So, the required numbers are (13 * 1, 13 * 12) and (13 * 3, 13 * 4).
Clearly, there are 2 such pairs.