Log9(49)*log7(5)*log25(27)*log36(6)

Здесь нужен переход к другому основанию и :
а) log 49 = 2log7
    основания = 9
б) log 27 = 3 log3
    основания = 25
Начали:
2log 7·   log 5 ·  3  log 3·  ( log6/log36)=
осн-е9   осн-е7   осн-е 25   осн-я =6
=3 log 7· (log 5/log7) · ( log 3/log 25)=
  осн-е 9    осн-я 5             осн-я 5
=3/2·( log 7/log9)· log 3/log 7=3/4
            jcyjdfybz = 5

500 куб. м= 500 000 литров
1 куб дм = 1 л

300 л в минуту или 300·60=18 000 л в час наполняет 1 труба

Пусть вторая наполняет х л в час,третья у л в час.

Пусть сначала первая труба проработала t часов, а вторая и третья вместе в два раза больше, т.е 2 t часов
18 000·t + 2t·(x+y)=500 000
12,5(x+y)=18 000t

Выражаем (х+у) из второго уравнения  (x+y)=18 000·t/12,5
и подставляем в первое:

18 000 t + 2t·1 440t=500 00
или
36t²+225t-6250=0
a=36, b=225, c=-6250

D=b²-4ac=225²+4·36·6250=950625=975²
t₁=(-225-975)/2<0
t₂=(-225+975)/72=750/72=10 целых 30/72 часа=
=10 целых 5/12= 10 целых 25/60=10 часов 25 минут

ответ. Первая труба работала10 часов 25 минут

1. proximately twenty years ago children wore strictly school uniform at school. but since the 1990s school uniform has been cancelled. children chose themselves a school dress. anyway, many schools nowadays have school uniform. is it good or had? this question has both advantages and disadvantages.now, let`s consider positive aspects.firstly, the school uniform has strictness which make children study at school more seriously.further more, school uniform makes children more disciplined.more than that it isn`t very expensive. and every family can afford to buy it.more over, school uniform removes social inequality because both rich and poor children wear the same clothes.further more, there is no such a question what to put on in the morning. now, let`s pay our attention, to same negative aspects.school uniform prevents children to be individuality. all are a like. one more, every day one and the same clothes.by the end of the school year it becomes untidy and not pleasant to look at. all in all school uniform has advantages and disadvantages, but as for me personally i vote for the school uniform because i presume it convenient for pupils.извини второе не могу у меня мозг не компьютер