Bamboo shoots double in height every day from germination to adulthood. 10 days to grow to 40 decimeters, how many days does it take for bamboo shoots to grow to (5/2) decimeters?
竹笋从发芽到长成，每天长高一倍．10天长到40分米，问竹笋长到(5/2)分米需要多少天天．
<result>6</result>