Упростите выражение и найдите его значение 1/2а+1/3а-1/4а если а 1 5/7 Ответ должен быть таким 7/12

1) subjects, laboratories, classes, books, dictionaries, translations, tape-recorders, lessons, shelfs, children, grown ups, film-strips, schools, institutes, teachers, reports, colleges, marks, circles, stories, examinations 2)languages, representatives, professions 2. text, questions3.questions4.books5. formations, tenses, voice 6. passage7.songs3)marks, subjects2.examinations3.subject4.grown ups, children5.schoolmates, teachers6.books7.books8.students

1A subject - subjects; a laboratory - laboratories; a class - classes; a book - books; a dictionary - dictionaries; a translation - translations; a tape-recorder - tape-recorders; a lesson - lessons; a shelf - shelves; a child - children; a grownup - grownups; a film-strip - film-strips; a school  - schools; an institute - institutes; a teacher - teachers; a report - reports; a college - colleges; a mark - marks; a circle - circles; a story - stories; an examination - examinations.2Languages, representative, professionsText, examples, rule, questionsQuestionsBooksCharacterFormations, tenses, voicePassageSongs3Marks, subjectsExaminationsSubject4Grown-ups, childrenSchoolmates, teachersBooksBooksStudents.

(1/2+1/3-1/4)*а=6/12+4/12-3/12=7/12а

1/2а+1/3а-1/4а=а(1/2+1/3-1/4)=7/12а если а = 1 5/7, то 7/12а=7/12х1 5/7=7/12х12/7=1.