×÷9=1000-910 ו9=1000-910 , 100•×=2430-2030 100÷×=2430-2430

1) x : 9 = 1000 - 910
x : 9 = 90
x = 90 * 9
x = 810

2) x * 9 = 1000 - 910
x * 9 = 90
x = 90/9
x = 10

3) 100 * x = 2430 - 2030
100 * x = 400
x = 400/100
x = 4

4) 100 : x = 2430 - 2430
100 : x = 0
x = 100/0
решение не имеет