3. 大于700的三位整数中，有多少是奇数，要求每个数字都不为零，且每位数字都不同。答案： 91 How to get the answer?
4. is xy>z?
(1). xyz=1 (2). xyz^2>1 我觉得是C,可是很多大侠说是E,请教。
19.长方形，周长P，面积K，哪个一定对？
答案是2w^2-pw+2k=0.可是不会算
22．On Jane’s credit card account, the average daily balance for a 30-day billing cycle is the average of the daily balances at the end of each of the 30 days.At the beginning of a certain 30-day billing cycle,Jane’s credit card account had a balance of $600.Jane made a payment of $300 on the account during the billing cycle.If no other amounts were added to or subtracted from the account during the billing cycle, what was the average daily balance on Jane’s account for the billing cycle?
1) Jane’s payment was credited on the 21st day of the billing cycle.
2) The average daily balance through the 25th day of the billing cycle was $540.
The key is D,but why?
31. The three digits number is K, what is the number of tenths of K?
a. the sum of tenths of K plus 9 is 3.
b. the sum of tenths of K plus 4 is 2.
