Answer: 10 hours
Step-by-step explanation:
The 10hp pump takes x hours to empty the pool which means it gets [tex]\dfrac{1}{x}[/tex] of the job done in one hour.
The 6hp pump takes x+5 hours to empty the pool which means it gets [tex]\dfrac{1}{x+5}[/tex] of the job done in one hour.
Together, they can get [tex]\dfrac{1}{x}+\dfrac{1}{x+5}[/tex] of the job done in one hour.
It is given that together they get the job done in 6 hours which means they get [tex]\dfrac{1}{6}[/tex] of the job done in one hour.
10 hp pump + 6 hp pump = Together
[tex]\dfrac{1}{x}\quad +\quad \dfrac{1}{x+5}\quad =\quad \dfrac{1}{6}[/tex]
Multiply by 6x(x+5) to eliminate the denominator:
[tex]\dfrac{1}{x}(6x)(x+5) +\dfrac{1}{x+5}(6x)(x+5) = \dfrac{1}{6}(6x)(x+5)[/tex]
Simplify and solve for x:
6(x + 5) + 6x = x(x + 5)
6x + 30 + 6x = x² + 5x
12x + 30 = x² + 5x
0 = x² - 7x - 30
0 = (x - 10)(x + 3)
0 = x - 10 0 = x + 3
10 = x -3 = x
Since the number of hours cannot be negative, disregard x = -3.
So, the only valid answer is x = 10.
