Yes/No DS questions are the most common type of GMAT Quantitative questions. These require a statement to consistently be either Yes or No to be considered ‘Sufficient’. In Yes/ No DS questions, a range of values can establish sufficiency as long as the answer to the question is always Yes or always No.
For instance, if a question asks if x is greater than 0, a statement indicating that x is greater than 1 would be sufficient, even though many values of x satisfy the statement. It’s important to recognize that Yes/No questions do not require a Yes answer for sufficiency. Instead they require a consistent answer. For example, in the question asking if x is greater than 0, a statement indicating that x is less than -1 would be sufficient. The answer to the question would always be No. In Yes/No questions, it’s the word always that is most important. On the other side, a sometimes Yes, sometimes No answer is insufficient. Because of these variances, we’ll need to think a little bit differently when determining the type of information necessary to answer a Yes/No question. Some Yes/No questions will not call for a specific yes or no answer but will follow the same basic guidelines.
Let’s see this at work with a GMAT Question
Is 4 + (n/6) an integer?
While there’s no algebra that we can simplify here, we can mentally simplify this question by identifying what’s relevant to answering it. Since an integer plus another integer always produces an integer, the value of 4 is irrelevant to whether the expression produces an integer. The only part of this expression that matters is n over 6. Narrowing our focus makes everything clearer. When n is a multiple of 6, the answer to the question will always be yes. Therefore, we’re going to look for the information in the statements.
Looking at Statement (1), we see that n is a multiple of 3. This is insufficient because it doesn’t tell us if n is divisible by 6, only that it’s divisible by 3. We could plug in the number 3 for n and get 3 over 6, which answers the question with a NO, since 3 over 6 is not an integer. On the other hand, we could try n equals 6. 6 over 6 is an integer, so the answer would be yes. Since we have a yes answer and a no answer, this statement is insufficient. Eliminate answer choices (A) and (D).
Statement (2) tells us that n divided by 6 has a remainder of 0. This is just like letting us know that n is a multiple of 6. This is exactly what we are looking for, so it’s sufficient. The correct answer is (2) alone or answer choice (B).
All we need is to take the time to simplify the question stem to determine what’s really relevant to the question itself. In other words, Yes/No DS questions are, simply put, questions that call for a “Yes” or a “No” answer or both, to prove sufficiency.
For more Data Sufficiency strategies, read our blog post about Combining Statements.