题干

一艘轮船顺流航行98千米、逆流航行42千米时共用了8小时;当这艘轮船顺流航行72千米、逆流航行108千米时共用了12小时.问此艘轮船的速度是多少?如果两个码头相距315千米,则轮船往返一次需要多少小时?

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答案(点此获取答案解析)

解:①顺流速度是逆流速度的(98×3﹣72×2)÷(108×2﹣42×3)=
5
3
(倍).
②顺流速度为:(98+42÷
3
5
)÷8=21(

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    The “swim-with-dolphins” tourist industry is becoming more popular every year with the increase of people's income. After all, it can cost a large amount of money to have this kind of holiday experience. So tour operators try to place eager swimmers as near as possible to the dolphins by trying to predict where the dolphins will be.

    Research has shown that while dolphins can move away if they do not want to interact (交流) with human swimmers, they do not like it at all if the swimmers slip into the water directly on top of them or if humans are in their path of travel. However, if swimmers enter the water to one side of them, the dolphins do not avoid the swimmers to the same extent.

    In all cases, the dolphins seem to have become more sensitive to the presence of the swimmers. For dolphins, swimming amongst or with humans is not necessarily a high priority. This research has shown that only 19% of any group of dolphins will participate in interaction. Young dolphins are the most likely to interact; they do seem curious about being with humans. It is believed that they see humans as “entertainment” and that the interaction is a new and unusual experience for them.

    It is frequently asked whether “swim-with-dolphins” tourism should be discontinued. The advice is that dolphins should be given enough periods of time throughout the day when they are not exposed to tourism. Permitted interactions should not be too disturbing to the dolphins since there could be mothers and calves (幼崽) present in dolphin groups. There should also be educational campaigns about the creatures and what is likely to cause danger to them.

    It is not easy to explain to someone that they cannot fulfill their lifelong dreams because the dolphins are resting, or that a mother dolphin and calf are in the area. But if we are to enjoy these remarkable animals and not just use them for our entertainment, then we must carefully monitor the “swim-with-dolphins” industry worldwide.