Data sufficiency: the method

What the item asks

Bocconi lists data sufficiency as the second kind of data insight item: a problem followed by two statements, numbered (1) and (2), where you decide which of them are necessary, if any, to answer it. You are not asked for the answer itself. You are asked whether the information could settle it.

That changes how you work. You stop as soon as you know whether a unique answer exists. Solving to the final number is wasted time, and on a test without a calculator, time spent on arithmetic you did not need is time taken from another question.

About the answer choices

Bocconi does not publish the current wording of its data sufficiency choices. A 2024 sample from Bocconi used four choices, one of which covered either statement being enough on its own, but the form of the test may have changed since. So this lesson teaches the logic, which does not depend on the wording, and the checks on this page use our own four options:

• statement (1) alone is enough; statement (2) alone is not;
• statement (2) alone is enough; statement (1) alone is not;
• both statements together are enough; neither alone is;
• even both statements together are not enough.

Our checks are built so that the fifth possible case, each statement being enough on its own, never arises. On the test, read the choices once and map them onto the five cases below.

The five possible outcomes

Every item ends in exactly one of these:

(1) alone	(2) alone	Together	Outcome
enough	not enough	–	(1) alone
not enough	enough	–	(2) alone
enough	enough	–	each alone
not enough	not enough	enough	both together
not enough	not enough	not enough	not enough

If one statement alone is enough, you never need "both together": the right choice always names the least information that settles the question.

Step 1: restate the question

Before reading the statements, write down exactly what would settle the question. Two kinds:

• Value questions ("What is $x$?", "How many…?") are settled only by one value. Two possible values is not enough.
• Yes/no questions ("Is $n$ odd?", "Did sales exceed…?") are settled by a definite answer, yes or no. A statement that proves the answer is always "no" is enough; only "sometimes yes, sometimes no" is not.

Often the restatement simplifies the work: "What is $x + y$?" needs only the sum, not $x$ and $y$ separately.

Step 2: statement (1) alone

Forget statement (2) completely. Does (1), with the facts in the question, fix the value or the yes/no answer? If you can think of two cases that fit (1) and give different answers, (1) is not enough.

Step 3: statement (2) alone

Now forget (1), which is the hard part: information from (1) leaks easily into your reading of (2). Test (2) with the question's facts only.

Step 4: together, only if needed

If neither alone is enough, combine them. Remember that the statements are always true and never contradict each other. Two statements that say the same thing in different forms (one is a multiple of the other) add nothing together.

Testing with cases

The fastest way to show a statement is not enough is to find two cases that satisfy it and give different answers. For yes/no questions try a case that gives "yes" and then hunt for one that gives "no". If you search honestly and every case gives the same answer, look for the algebra that proves it.