Target Test Prep Sample GCF and LCM Question

Example 1

easy

If p and q are integers greater than zero, what is the value of pq?

1) The least common multiple of p and q is 240.

2) The greatest common factor of p and q is 8.

Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient.
Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient.
BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient.
EACH statement ALONE is sufficient.
Statements (1) and (2) TOGETHER are NOT sufficient.
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Solution:

Question Stem Analysis:

We need to determine the value of pq.

Statement One Alone:

⇒ The least common multiple of p and q is 240.

This tells us the smallest number that both p and q will divide into is 240. This is not enough information to determine the value of pq because there are multiple values of p and q that have an LCM of 240. For example, 15 and 16 have an LCM of 240, and 60 and 80 have an LCM of 240. Statement one alone is not sufficient.

Eliminate answer choices A and D.

Statement Two Alone:

⇒ The greatest common factor of p and q is 8.

This tells us the largest number that will divide into p and q is 8. That is, 8 is the largest factor that p and q share. This is not enough information to determine the value of pq because there are multiple values of p and q with a GCF of 8. For example, the GCF of 16 and 24 is 8, and so is the GCF of 24 and 32. Statement two alone is not sufficient.

Eliminate answer choice B.

Statements One and Two Together:

It must be true that LCM(p, q) × GCF(p, q) = pq. Thus, pq = 240 × 8 = 1,920. Both statements together are sufficient to answer the question.

Correct answer:C