According to probability principle of multiplication, the survival rate was the product of retention rate at certain period and survival rate at the previous period.
根据乘法概率法则，将某一年龄段的留存率与前一年龄段的生存率相乘可得该年龄段的生存率。
2
Compared with the prior art, the utility model has the advantages of low probability of dirt retention and convenient cleaning.