Even though such a question will never appear on GMAT, there is a great learning here - when you think something is impossible, you just have to cool off , relax your mind and start thinking afresh.
The moment I heard 'using only 0s', my first instinct was 'what!? You can add/subtract/multiply/divide whatever, you will never get any other number'. So then I thought that since there has to be a solution, I am missing something so I should back up and review what I know. Then, all I wanted to do was to figure out an operator which I could use with 0 to give me another number. That's when 0! came to mind and as you can see, after that all you need is 5 secs to fit it in 120. I do hope your takeaway from this question is this:
When you read a Problem Solving question and think that it cannot be solved, all you need to do is keep your cool and think about the first thing you need to figure out. Other steps will follow automatically. You know that it can be done so you can do it too.
(Disclaimer: I do not advice you to waste too much time on any one question during the actual exam. In the actual exam, sometimes, you might need to say, "I know we can solve it but I don't think I can in the given time frame so I should instead move on to the next question." You can take your time during practice at home.)
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