Jen walked along a track at an average speed of 100 meters per minute

题目

Jen walked along a track at an average speed of 100 meters per minute. Was the length of the track greater than half a kilometer? (1 kilometer = 1000 meters)

(1) She took more than 250 seconds to cover the track.

(2) She took less than 290 seconds to cover the track.

选项

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.

解析

珍的速度 = 60秒跑100米 = $\frac{5}{3}$ 米/秒我们需要判断的问题：**跑道长度是否大于500米？** **条件1：** 她跑完整个跑道用时超过250秒。若用时为250秒，那么跑道长度 = $\frac{5}{3} \times 250 = 416.67$ 米。由于实际用时超过250秒，假设用时达到300秒，此时跑道长度就会超过500米。因此，通过该条件会得出两种不同的答案。 **结论：条件1不充分** **条件2：** 她跑完整个跑道用时不到290秒。对于任何小于290秒的用时，跑道长度必然小于500米。因此，我们可以确定地得出结论：跑道长度**不大于**500米。 **结论：条件2充分** **答案：选项B**

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