Question

Две трубы на­пол­ня­ют бас­сейн за 8 часов 45 минут, а одна пер­вая труба на­пол­ня­ет бас­сейн за 21 час. За сколь­ко часов на­пол­ня­ет бас­сейн одна вто­рая труба?

Answer 1

8ч 45мин= 8 3/4ч= 8,75ч
Бассейн =1
Первая труба 1бассейн за 21ч
Вторая труба за ?ч
Первая в час = 1:21=1/21часть заполнит

Делим 1 бассейн на время двух труб и вычитаем 1 трубы время в час.

1))
1/ (8 3/4) - 1/21=
1/ ((8•4+3)/4)- 1/21=
1/(35/4)- 1/21= 1•4/35- 1/21=
(4•3)/(35•3)- (1•5)/(21•5)=
12/105- 5/105= 7/105= 1/15 часть заполняет вторая труба

2)) 1: 1/15= 1• 15/1= 15 часов надо 2 трубе

Ответ: за 15 часов вторая труба заполнит бассейн


С икс
Х=время второй трубы
21час=время 2 трубы
Всего 8 3/4ч
Бассейн =1
1/Х+1/21=1/ (8 3/4)
1/Х= 1/((8•4+3)/4)- 1/21
1/Х= 1/(35/4)- 1/21
1/Х= 1• 4/35- 1/21
1/Х= (4•3)/(35•3) - (1•5)/(21•5)
1/Х=12/105-5/105
1/Х=7/105=1/15
1/(1/15)=Х
Х=1•15/1
Х=15 часов

Ответ: вторая труба заполнит за 15 часов бассейн

Answer 2

Problem Analysis

We are given that two pipes can fill a pool in 8 hours and 45 minutes, and one of the pipes can fill the pool in 21 hours. We need to determine how long it would take for the second pipe to fill the pool on its own.

Solution

Let's assume that the first pipe can fill the pool in x hours. We can set up the following equation based on the given information:

1/x + 1/21 = 1/(8 hours and 45 minutes)

To solve this equation, we need to convert the time of 8 hours and 45 minutes into hours. Since there are 60 minutes in an hour, 45 minutes is equal to 45/60 = 0.75 hours.

Substituting the values, we have:

1/x + 1/21 = 1/(8 + 0.75) = 1/8.75

To simplify the equation, we can find a common denominator:

(21 + x)/(21x) + 1/21 = 1/8.75

Multiplying both sides of the equation by 21x, we get:

21 + x + x = 21x/8.75

Simplifying further:

21 + 2x = 2.4x

Subtracting 2x from both sides:

21 = 0.4x

Dividing both sides by 0.4:

x = 21/0.4 = 52.5

Therefore, the first pipe can fill the pool in 52.5 hours.

To find out how long it would take for the second pipe to fill the pool on its own, we can subtract the time taken by the first pipe from the time taken by both pipes together:

Time taken by the second pipe = Time taken by both pipes - Time taken by the first pipe = 8 hours and 45 minutes - 52.5 hours

Converting 8 hours and 45 minutes into hours, we have:

8 hours and 45 minutes = 8 + 45/60 = 8.75 hours

Therefore, the time taken by the second pipe to fill the pool on its own is:

8.75 hours - 52.5 hours = -43.75 hours

Since the result is negative, it implies that the second pipe cannot fill the pool on its own.

Answer

The second pipe cannot fill the pool on its own.