求助 1道prep maths ！

linlin3151

149. 

A certain library assesses fines for overdue books as follows.  On the first day that a book is overdue, the total fine is $0.10.  For each additional day that the book is overdue, the total fine is either increased by $0.30 or doubled, whichever results in the lesser amount.  What is the total fine for a book on the fourth day it is overdue?

 

(A) $0.60

(B) $0.70

(C) $0.80

(D) $0.90

(E) $1.00

为什么答案是B呢

怎么我算出来就是C呢？

向大家求助，谢谢！

sunjueliang

第一天是0.1，第二天要么*2，要么+0.3，以小的为准。

那么第二天就是0.1*2=0.2（而不是0.1+0.3=0.4因为0.4>0.2)，第三天就是0.2*2=0.4(而不是0.2+0.3=0.5因为0.4小一点），第四天就是0.4+0.3=0.7（而不是0.4*2=0.8因为0.7小一点）。hope that helps.

linlin3151

That really helps!
Thank you so much!