数学题目

Whenever Martin has a restaurant bill with an amount between USD10 and 99, he calculates the dollar amount of the tip as 2 times the tens digit of the amount of this bill, if the amount of Matin's most recent restaurant bill was between USD 10 and 99, was the tip calculated by Matin on this bill greater than 15% of the amount of the bill?

(1) The amount of the bill was between USD 15 and USD 50
(2) The tip calculated by Matin was USD 8
请教这个题目什么意思？tens digit of the amount?怎么考虑这个题目？谢谢

个人算法，不知道对不对~~~~

 tip as 2 times the tens digit of the amount of this bill

1）tip: 2 x 1=2, 2 x 5=10 tip是2-10, 2/10=20% 10/99=10% tip: 10%-20%

2）tip是8， 8/10=80% 8/99=8%，tip:8%-80%

1)+2):10%-20%

是不是选E阿~~~

我来试试：

 这道题目是问一个大于10小于99的帐单，小费是按其十位数的两倍计算。问：是否小费比帐单总额的15%大？

（1）不行。我们举两个数：当bill为50时，t=10>0.15*50; 当bill=15，t=2<2.25

（2）可行。此时，t=8,   40<=bill<=49,6<= 0.15BILL<7.5<8.

答案：B