На верхней полке 12 книг а на нижней 8 сколько книг надо переложить с верхней полки на нижнюю чтобы чтобы книг на этих полках стояло ровно

2 книги надо переложить на вторую полку 

Эта задача решается уравнением, или алгебраическим
Пусть х - это будет 2 число,то тогда 7/12 будет первым числом, а третьим числом - 2 1\6 * х
2 1\6*х=13\6=26\12
26\12х
7\12х+х+2 1\6х=315
7\12х+12\12х26\12=315
Переводим смешанную дробь 2 1\6 в обыкновенную)
(12\12=1)
45\12х=315
х=315:45\12
х=(315*12):45
х=84.
84 - мы узнали второе число.
Теперь от этого ответа, мы можем узнать первое и третье число.
7\12*84=588\12=49\1=49
49 - первое число.
13\6*84=1092\6=182\1=182
182 - третье число.
ответ: 1-ое число - 49, 2-ое число - 84, 3-е число - 182.

An engineer is a specialist with a higher technical education. The name of the profession comes from the Latin word ingenium, which means "ability, ingenuity." Engineering professions are among the most massive professions of highly skilled labor. Engineers work in many branches of the national economy: in factories, construction sites, mines, in military affairs, aviation, transport, they are developing in research institutes. The circle of engineering positions is wide: it is a master or a senior master, an engineer and a senior engineer, a shift supervisor, a site, a leading engineer or an enterprise manager.
History of the profession: Engineers were originally called people who run military vehicles. The first civil engineers in the 16th century were builders of bridges and roads, and the first educational institutions for training engineers appeared a century later. The specialty of an engineer came to Russia thanks to Peter I. By now the system of training and professional activity of engineers is represented by a whole range of specialties ...The social importance of the profession in society: In our country, the profession of an engineer is one of the most common: it is represented by more than a third of specialists with higher education. This is not accidental, because it is the engineer who takes part in the production of various material goods - from everyday goods and food products to sophisticated machinery.