1 математика номер 1 900 - икс: 5 = 800 3 умножить икс - 80 : 4 = 25 номер 2 (580 - икс) : 4 = 100 40 : икс + 70 = 90

1). 900 - x : 5 = 800

900 - 800 = x : 5

100 = x : 5

x = 100 * 5

x = 500.

(3 * x - 80) : 4 = 25

3 * x - 80 = 25 * 4

3 * x - 80 = 100

3 * x = 100 + 80

3 * x = 180

x = 180 : 3

x = 60.

3 * x - 80 : 4 = 25

3 * x - 20 = 25

3 * x = 25 + 20

3 * x = 45

x = 45 : 3

x = 15.

2). (580 - x) : 4 = 100

580 - x = 100 * 4

580 - x = 400

580 - 400 = x

x = 180.

40 : x + 70 = 90

40 : x = 90 - 70

40 : x = 20

x = 40 : 20

x = 2.