Hey Deepti,
This is a very very tough one. I worked on it earlier also, but didn't get to it.
The conclusion was:
The hypotenuse on the top is slightly convex (turquoise triangle has greater slope than red).
Hence when they are swapped, the top is slightly concave, thus the mass is "used up" faster. Fast enough to make way for the hole, but slow enough to not be easily noticable.
In short, the two figures are actually quadrangles; not triangles.
Yes aastha you are right, proving that you are an infosian.
next riddle
What force and strength
cannot get through,
I, with a gentle touch, can do;
And many in these twisted halls would stand,
Were I not, as a friend, at hand...
I tie and hold, capture and bind,
yet both knights and knaves doth crave me.
I faithfully enslave all within my grasp,
whether or not they seek me.
Yet those who have never felt my unmerciful hand,
are pitied by their fellow Man...
