Hi Sri,

This question is essentially about the relationships between small, medium and large containers. Instead of trying to solve this with complex equations, I'm going to go about this in as easy a way as I can.

From the prompt we know that....

L = 3M 1 large = 3 medium
L = 5S 1 large = 5 smalls

We also know that we have the equivalent of 90 medium containers full of soap. Using the above information, we know that we would have 30 full large containers OR 150 small containers

The question asks us to have an EQUAL number of large and small containers, so we have to "move soap" around until we have the same total amount of soap as can fill 90 mediums, BUT have an equal number of large and small containers.

We'll start with....
30 larges and 0 smalls

For every large container we remove, we gain 5 smalls
29 large and 5 smalls
28 large and 10 smalls
27 large and 15 smalls
26 large and 20 smalls
25 large and 25 smalls

And then we're done.

GMAT assassins aren't born, they're made,
Rich