Lets check how fast you can solve this:

You wanted to buy a T-shirt worth Php97.

Because you have no money, you borrowed Php50 from your sister and another Php50 from your brother.  You now have in your pocket  a total cash of Php100.

Since the shirt  was only worth Php97, you still got a change of Php3. You returned the Php1 to your sister and the other Php1.00 to your brother. That leaves you  with Php1. And you still owe your sister Php49 and your brother Php 49.

Now here is the question:

PhpP49+Php49.00 = Php98 plus Php1 in your hands equals Php99.
The total money is Php100.
Where is the missing peso?