It takes 2 days for a passenger ship to travel downstream from Shashi to Wuhan, and 3 days to travel upstream from Wuhan. How many days does it take for a raft to sail downstream from Shashi to Wuhan?
一客轮从沙市顺流而下开往武汉需要2天，从武汉逆流而上需要3天，一木筏从沙市顺流漂行要几天到达武汉？
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