X-10=70

x      =70+10

x      =80                  vậy x là 80

x:3:2=9

x=9x2x3

x=54

All all the number of class is:

  (1000 - 1):1+1=1000(numbers)

The sum of all integers from 1 to 1000 is:

 (1000+1)x1000:2=500500

Answer:500500