ICC World T20 2012 super 8 stage will be over soon.
The results in group 2 were:
Pak beat SA by 2 balls.
Aus beat Ind by 31 balls.
Aus beat SA by 14 balls.
Ind beat Pak by 18 balls.
Pak beat Aus by 18 balls.
Ball Difference for Pak is 2-18+18=2.
Ball Difference for India is -31+18=-13. Winning by 16 balls will take them to semi-final stage.
Batting first, assuming they bat 20 overs, India needs to defend the score after 17.2 overs. That simple!
UPDATE : After 17.2 overs, India scored 121/5 so India would have qualified by defending 120. India finished at 152/6 and needed to win by 31 runs to qualify based on Net Run Rate hence defending 121. It is a chance but the proximity of 120 & 121 indicate that both methods are similar (not same) but one uses an accumulative unit (a ball), easily understood by all cricket enthusiasts and another uses a Rate involving unnecessary arithmetic.