48. At the eating contest the winner ate an average of 15 hot dogs at the first 20 sittings. After a further 20 sittings the average increased to 20 hot dogs. What was the average for the last 20 sittings?
A.15.
B. 20.
C. 25.
D. 30.
49. A ball bearing is to be dropped into each of these beakers. In which experiment will the ball travel the slowest?
A. Experiment 1, because water at 20 degrees Fahrenheit is ice!
B. Experiment 2, because milk at 40 degrees Fahrenheit is ice!
C. Experiment 3, because oil at 60 degrees Fahrenheit is ice!
D. Experiment 4, because tar at 80 degrees Fahrenheit is ice!
50. Tanya can swim faster than Jack but slower than Sally. Harry usually swims faster than Jack, sometimes swims faster than Tanya, but never swims faster than Sally. Who is the slowest swimmer?
A. Tanya. B. Sally.
C. Harry. D. Jack.
请翻译并讲讲为什么。谢谢！
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