Brain teaser for the week 20200905 每周烧次脑
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Suppose a car goesuphill a distance of 1 mile, then immediately turns around and goes downhillthe same distance, and sup-pose the average rate of the car for the whole tripis 20 miles per hour. What is the total time spent going uphill and downhill inminutes?
(a) 6
(b) 8
(c) 10
(d) Cannot be determined unless the time going downhill is given
(e) Cannot be determined unless the speed going uphill is given
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Answer to the last week 上期答案 Brain teaser for the week 20200829 每周烧次脑
(c) 2/3
Probability can be defined as the favorable number of possible outcomes divided by the total number of possible outcomes. Since one of the coins lands as a head, the total number of ways this is possible is the following:
five-cent head, ten-cent tail
five-cent head, ten-cent head
five-cent tail, ten-cent head
There couldn’t be a possibility of a five-cent tail, ten-cent tail combination because we are told that one of the coins must be a head.
So there are three possibilities.
Now, the favorable ways that the five-cent coin will land as a head are:
five-cent head, ten-cent tail
five-cent head, ten-cent head
That is two ways out of three possible ways. Thus, the probability is 2/3.
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