1. What is the units digit of 5x3? Where x is a positive even integer.
2. 估算 x+106y+1012z (1﹤x﹤y﹤z﹤2)
3. What is the remainder when 3100 is divided by 8?
4. What is the unites digit of 2321-23?
5. 24 is an integer which is divisible by its units digit, how many integers which can be divisible by their unites digit from 10 to 70?
A: the range of seven consecutive integers
7. How many integers which cannot either divisible by 3 or 7 from 1 to 100, inclusive?
8. (a+b/d)/(d/c)，问原式中，a b c d谁double，原式子的值也会double
10. The speed of Tom’s car is 60 miles per hours from home to his work place, and the speed of the car is 40 miles per hours from work place to his home, the total hours he spend on the road is 2.5 hours, how many miles from his home to the working place?
11. a 完成一项工作需要3t, b需要t, 两个人一起工作需要多久, in terms of t?