Scientists fed a worm in the laboratory. The worm grew very fast. From larva to adult, it doubled in size every day, and it grew to 8 centimeters in 8 days. How many days did it take for the larvae to grow to 2 cm?
科学家在实验室里喂养了一条虫子，这条小虫生长速度很快，从幼虫到成虫，每天都长大1倍，8天就长到8厘米长了．当幼虫长到2厘米时，用了多少天．
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