Manhattan GMAT Challenge Problem of the Week – 1 June 2010

by Manhattan Prep, Jun 1, 2010

Heres the latest Challenge Problem! As always, the problem and solution below were written by one of our fantastic instructors. Each challenge problem represents a 700+ level question. If you are up for the challenge, however, set your timer for 2 mins and go!

Question

The three-digit positive integer n can be written as ABC, in which A, B, and C stand for the unknown digits of n. What is the remainder when n is divided by 37?

(1) A + B/10 + C/100 = B + C/10 + A/100

(2) A + B/10 + C/100 = C + A/10 + B/100

a. Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient.

b. Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient.

c. BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient.

d. EACH statement ALONE is sufficient.

e. Statements (1) and (2) TOGETHER are NOT sufficient to answer the question asked, and additional data are needed.

Answer

The question stem tells us that the positive integer n has three unknown digits: A, B, and C, in that order. In other words, n can be written as ABC. Note that in this context, ABC does not represent the product of the variables A, B, and C, but rather a three-digit integer with unknown digit values. It is important to note that since A, B, and C stand for digits, their values are restricted to the ten digits 0 through 9. Moreover, A cannot equal 0, since we know that n is a three-digit integer and therefore must be at least 100.

We are asked for the remainder after n is divided by 37. We could rephrase this question in a variety of ways, but none of them are particularly better than simply leaving the question as is.

Statement (1): SUFFICIENT. We can translate this statement to a decimal representation, which will be easier to understand. The left side of the equation, in words, is A units plus B tenths plus C hundredths. We can write this in shorthand: A.BC (that is, A point BC). After performing the same translation to the right side of the equation, we can see that we get the following:

A.BC = B.CA

Since A, B, and C stand for digits, we can match up the decimal representations and observe that A = B and B = C. Thus, all the digits are the same.

This means that we can write n as AAA, which is simply 111 A.

Now, 111 factors into 3 37, so n = 3 37 A. Thus, n is a multiple of 37, and the remainder after division by 37 is zero.

Statement (2): SUFFICIENT. Again, we can match up the decimal representations of the given equation and find that all the digits are the same. The logic from that point forward is identical to that shown above.

The correct answer is (D): EACH statement ALONE is sufficient.

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