单选题 Khalil drove 120 kilometers in a certain amount of time. What was his average speed, in kilometers per hour, during this time?(1) If Khalil had driven at an average speed that was 5 kilometers per hour faster, his driving time would have been reduced by 20 minutes. (2) If Khalil had driven at an average speed that was 25% faster, his driving time would have been reduced by 20%.

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.

【正确答案】 A

【答案解析】Let r be Khalil’s average speed in kilometers per hour and let t be Khalil’s time in hours. Thenrt = 120, or t =120/r. What is the value of r ?(1) If Khalil’s speed had been (r + 5) kilometers per hour, then his driving time would havebeen (t-1/3) hours. (r + 5) ( t -1/3) = 120 Statement (1)