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 = 2 430 – 2 030
100 · x = 400
x = 400 : 100
x = 4
4) 100 : x = 2 430 – 2 420
100 : x = 10
x = 100 : 10
Ответ: 810; 10; 4; 10