Условие:

Реши уравнения.
x : 9 = 1000 − 910;
x * 9 = 1000 − 910;
100 * x = 2430 − 2030;
100 : x = 2430 − 2420.

x : 9 = 1000 − 910
x : 9 = 90
x = 90 * 9
x = 810
 
x * 9 = 1000 − 910
x * 9 = 90
x = 90 : 9
x = 10
 
100 * x = 2430 − 2030
100 * x = 400
x = 400 : 100
x = 4
 
100 : x = 2430 − 2420
100 : x = 10
x = 100 : 10
x = 10