Inacertaintownsomepeoplewereaffectedbya’flu’epidemic.Inthefirstmonth20%ofthepopulationcontractedthefluwhilst80%werehealthy.Inthefollowingmonth20%ofthesickpeoplerecoveredand20%ofthehealthypeoplecontractedt

Question

In a certain town some people were affected by a ’flu’ epidemic.In the first month 20% of the population contracted the flu whilst 80% were healthy.
In the following month 20% of the sick people recovered and 20% of the healthy people contracted the disease.
What fraction of the population is healthy at the end of the second month?

Answer 1

在一座城里一些人受流感的影响.在第一个月20%的人口感染了流感仅有80%是健康的.
在接下来几个月20%的病人恢复和20%的健康的人感染疾病.
那么第二个月结束有多少人是健康的?
第一个月结束：20%患病,80%健康
第二个月结束：康复的人：20% x 20%=4%
依旧健康的人：（1-20%）x 80%=64%
所以第二个月结束健康的人有：64%+4%=68%