Hi chaitanya.bhansali,
This is more of a logic question than anything else. We need to be clear on the facts given to us and find the "worst-case" scenario (what number of balls would GUARANTEE that 5 different colors were picked?).
With a total of 55 balls and the progression described (1, 2, 3, etc.), you can determine that the number of each color would be....
1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 + 10 = 55
So we have 10 different colors.
As we pull balls from the bag, the only way to GUARANTEE that 5 different colors are chosen is to figure out the worst-case possibility (the maximum you COULD pick before you found the 5th color)....
If we picked the 10 balls of the same same color, then we'd only have 1 color, then....
If we picked the 9 balls of the same same color, then we'd only have 2 colors, then...
If we picked the 8 balls of the same same color, then we'd only have 3 colors, then...
If we picked the 7 balls of the same same color, then we'd only have 4 colors, then....
We'd need just 1 more ball, of any color, to end up with 5 colors...
10 + 9 + 8 + 7 + 1 = 35
We would need to pull 35 balls to GUARANTEE that we ended up with 5 different colors.
Final Answer: D
GMAT assassins aren't born, they're made,
Rich
