When faced with discovery questions that aren't perfectly phrased so as to be completely clear and unambiguous, responding parties or their attorneys are often tempted to answer the precise question asked rather than furnish the obviously-intended information, or to blow off the request with the "vague, ambiguous, etc." response.

While in some cases it may be permissible to to one or the other, even appropriate, I suggest that in most cases it is better to provide a response that furnishes the answer to the question the other side pretty clearly intends to be asking, even if the phraseology of the question is so tight and restrictive, or so loose and vague, that the evasive answer (or non-answer) could be given. A good-faith attempt to provide the information manifestly being sought is warranted, even if the question is goofy.

Nevertheless, there are limits to a resonding party's duty to interpret poorly-worded questions. Knowing what to answer is a skill lawyers develop over the years, supplemented by a good understanding of the facts of the client's case.

In the example you give, "open an account" would literally refer to THE ACCOUNT and also to each of the other 14+ accounts. I would think an answer along the following lines might be considered:

"I have asked Bank to open more than 15 accounts for me over the years. In most cases, Bank has obliged me; once or twice they turned me down for various reasons. With respect to Account No. 123-456789, I did apply to open the account which was given that number by Bank upon its opening, in or about November, 1993."

At least with respect to THIS question, as I understand it and with no knowledge of the case or the opposing party, I think an answer along these lines is more appropriate than objection on the ground of vague and ambiguous.

I would just add that specifically when it comes to requests for admissions, after stating any objections the responding party is obligated to admit or deny so much of the request as the responding party is capable of admitting or denying. If you wrongfully object to an RFA it can be deemed admitted, and if you deny facts the other side eventually proves true, they can recover their attorneys fees.