IIT JEE Advanced 2006 Paper 1

We have LCM of (p, q) = r2s4t2. Now, the distribution of r in p and q is listed as follows:

That is, the total cases is 6 – 1 = 5 and the repeated case is 1.
The same distribution of 5 and t in p and q is done by 9 and 5 ways.
The total number of ordered pairs (p, q) is 5 × 9 × 5 = 25 × 9 = 225