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Shkiper50 [21]
2 years ago
12

12. Of two inlet pipes, the smaller pipe takes four hours longer than the larger pipe to fill a

Mathematics
2 answers:
Mila [183]2 years ago
4 0

Step-by-step explanation:

l = large pipe

s = small pipe

s needs x hours alone to fill the pool.

l needs x-4 hours alone to fill the pool.

s does 1/x of the work in 1 hour.

l does 1/(x-4) of the work in 1 hour.

3 hours 45 minutes = 3.75 hours

3.75 × 1/x + 3.75 × 1/(x-4) = 1 (= the whole work)

3.75 + 3.75 × x/(x-4) = x

3.75×(x-4) + 3.75×x = x(x-4) = x² - 4x

3.75x - 15 + 3.75x = x² - 4x

7.5x - 15 = x² - 4x

-15 = x² - 11.5x

0 = x² - 11.5x + 15

the general solution to such a quadratic equation is

x = (-b ± sqrt(b² - 4ac))/(2a)

in our case

a = 1

b = -11.5

c = 15

x = (11.5 ± sqrt(132.25 - 4×1×15))/(2×1) =

= (11.5 ± sqrt(72.25))/2 = (11.5 ± 8.5)/2

x1 = (11.5 + 8.5)/2 = 20/2 = 10

x2 = (11.5 - 8.5)/2 = 3/2 = 1.5

x = 1.5 would turn l = 1/(x-4) negative, which does not make sense.

so, x = 10 is our solution.

that means

s does 1/10 of the work in 1 hour.

so, the small pipe alone fills the pool in 10 hours.

l does 1/(10-4) = 1/6 of the work in 1 hour.

so, the large pipe alone fills the pool in 6 hours.

Kipish [7]2 years ago
3 0

Answer:

6 hours

Step-by-step explanation:

Let the smaller pipe fill the pool in x hours and the bigger pipe y hours.

x-y=4

1/x+1/y=4/15

x=10, y=6

so 6 hours

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