请教几道gwd数学，冥思了好久（3）

1、if 10^50-74 is written as an integer in base 10 notation, what is the sum of the digits in that integer? (答案是440，算了很久是458)

2、one kilogram of a certain coffee blend consists of x kilogram of type I coffee and y kilogram of type II coffee. The cost of the blend is C dollars per kilogram, where C=6.5x+8.5y, is x<0.8

(1) y > 0.15

(2) C>= 7.3

3、the annual interest rate earned by an investment increased by 10% from last year to this year. If the annual interest rate earned by investment this year was 1%, what was the annual interest rate last year? (key 9.1%)

第三题盼解答

1. 10的50次方是1后面50个零，减去74变成51（总位数）-1（减一位）-2（个位和十位）=48个9，1个2，1个6，48*9+2+6=440

2.（1）X可以大于0.8也可以小于0.8，不符合
  （2）代入，当X=0.8，y=0.2时，C=5.2+1.6=6.9，此时C小于等于7.3，又因为Y的价钱更贵，所以X只能小于0.8，c才有可能大于等于7.3   选B

明白了，我觉得第二题，解方程可能清楚一些

(2) y=1-x，所以 c=6.5x+8.5(1-x)>=7.3, 方程解得 x<=0.6 所以x<0.8。

请问第三题呢

谢谢 lysun