Hi Ricky,

I shall try my best.

You are right - in the absence of additional information, one needs two equations to solve a linear equation in two unknowns.

However - there are some cases where additional information is given; in this case, the additional information is that x and y are integers. One has to buy either two stamps or three stamps. One cannot get 2.5 stamps.

Looking for such additional information which could be things like:

1. x and y are always integers, like in this case.

2. x could always be less than y, like in a question in which a kid eats y chocolates out of which x are pista chocolates.

3. one of either x or y could be an integer, like in a case where x refers to the number of kids in a competition

4. x is always a multiple of y, if the question states that y is the LCM of x

so on and so forth. I would be impossible to state an exhaustive list of possibilities.

The operative sentence is 'Look for additional information'.

Hope this helps.