A scientist places 29 cells in a petri dish.She knows the cells grow at an exponential rate,doubling in number every hour.How long will it take (in hours) for there to be 1200 cells in the dish?How long will it take to reach 140 cells?
问题描述：
A scientist places 29 cells in a petri dish.She knows the cells grow at an exponential rate,doubling in number every hour.
How long will it take (in hours) for there to be 1200 cells in the dish?
How long will it take to reach 140 cells?
答
29^(2n-2)=1200
n=1+log(下841)(上1200)
29^(2n-2)=140
n=1+log(下841)(上140)
答
这道题目的意思是每过一个小时,数量就翻倍.也即一个小时后,数量为29*2,两个小时后,为29*2*2...以此类推,n个小时后为29*2的N次方.那么要达到1200个,列出公式:29*(2的n次方)=1200
即n=㏒2(1200÷29),用计算器算出的n即为需要的时间.达到140个的时间只要将前边式子的1200换为140即可.