請問ㄧ題GMATprep

[EmmaCYC]

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?
(1)0.60
(2)0.70
(3)0.80
(4)0.90
(5)1.00
答案(2)0.7

我的想法是
increased by $0.30 => 0.1 => 0.4 => 0.7 => 1.0
doubled => 0.1 => 0.2 => 0.4 => 0.8
0.8<1.0(whichever results in the lesser amount)
所以選0.8
請問是哪裡有問題 還是我題目搞錯?
感謝!

[StanleyHuang]

每一天要用前一天的結果來算，而不是這兩種算法一直算下去。
所以第二天是 0.2元 (double)， 第三天是 0.4元 (double)，而第四天則是 0.7元 (increase)

[EmmaCYC]

原來是我的英文問題...
感謝!