Question

On a recent trip, Mary drove 50 miles. What was the average speed at which she drove the 50 miles?
(1) She drove 30 miles at an average speed of 60 miles per hour and then drove the remaining 20 miles at an average speed of 50 miles per hour.
(2) She drove a total of 54 minutes.

• 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.

Answer 1

Answer: (D)

Each statement alone is sufficient.

• If the time it took Mary to drive the $50$ miles can be determined, then her average speed can be determined by the formula of distance $=$ speed $\times$ time.
• From statement 1, it is given that she drove the first $30$ miles at an average speed of $60$ miles per hour, so she drove the first $30$ miles in hour. She drove the remaining $20$ miles at an average speed of $50$ miles per hour, so she drove the remaining $20$ miles in hours. Thus, she drove the $50$ miles in a total of hours, and thus her average speed for the $50$ miles can be determined.
• From statement 2, it is given that she drove a total of $54$ minutes, and thus her average speed for the $50$ miles can be determined.