х литров 55%-го раствора взяли для приготовления нового раствора;
0.55х - объем соли в 55%-ом растворе
(100-х) литров 30%-го раствора взяли для приготовления нового раствора
0.3(100-х) - объем соли в 30%-ом растворе
0,55х + 0.3(100-х) - объем соли в новом растворе
45% от 100 л = 0,45 * 100 = 45 объем соли в новом растворе
Уравнение.
0,55х + 0.3·(100-х) = 45
0,55х + 30 - 0.3х = 45
0,25х = 45 - 30
0,25х = 15
х = 15 : 0,25
х = 60 литров 55%-го раствора взяли
100 - 60 = 40 литров 30%-го раствора использовали для приготовления нового раствора.
ответ: 60л; 40л
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3x-x=18
2x=18
X=18:2
X=9 тетр в линейку
2) 9×3+9=36 всего тетр