а) (40*x) : 10=28 б) y:9-28=32 в) 39+490:k=46 г) (25-a) * 7=63

а) (40 * x) : 10 = 28;

40x : 10 = 28;

40x = 28 * 10;

40x = 280;

x = 280 : 40;

x = 7;

Проверим:

(40 * 7) : 10 = 28;

280 : 10 = 28;

28 = 28;

б) y : 9 - 28 = 32;

y : 9 = 32 + 28;

y : 9 = 60;

y = 60 * 9;

y = 540;

Проверим:

540 : 9 - 28 = 32;

60 - 28 = 32;

32 = 32;

в) 39 + 490 : k = 46;

490 : k = 46 - 39;

490 : k = 7;

k = 490 : 7;

k = 70;

Проверим:

39 + 490 : 70 = 46;

39 + 7 = 46;

46 = 46;

г) (25 - a) * 7 = 63;

(25 - a) = 63 : 7;

25 - a = 9;

-a = - 25 + 9;

-a = - 16;

a = 16;

Проверим:

(25 - 16) * 7 = 63;

9 * 7 = 63;

63 = 63;

Все верно.