Now I know why...

Krishna was made to fail the exam--- I mean if Pinky and Krishna both were shown as pass- then Pinky's lies would have never been unearthed but if Krihsna is failed and then while she struggles to unearth the truth, it will be revealed that Pinky's success is based on influence, and money and not only did she fail the interview but the exam as well...

even i think so...hope pinky's truth comes out soon

Yup, that would be the reason behind it. They have to show her finding out about who's behind everything (TTS, Bihari and even Pinky and her mom).