There are at least three packets of chips in the cup board.
∴ Total 10 packets in all.
∴ {Number of packets of chips, Number of packets of biscuits}
= {(3, 7) or (4, 6) or (5, 5) or (6, 4) or (7, 3) or (8, 2) or (9, 1) or (10, 0)}
The number of ways in which three packets of chips can be drawn
=3C3+4C3+5C3 +6C3+7C3+8C3 +9C3+10C3 = 330
The number of ways in which three packets of can be drawn when there are 9 packets of chips
=9C3==84∴ Required probability
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