Answer: it will take 9 hours to empty the pool.
Step-by-step explanation:
The pool is shaped like a rectangular prism with length 30 feet, wide 18 ft, and depth 4ft. It means that when the pool is full, its volume is
30 × 18 × 4 = 2160 ft³
If water is pumped out of the pool at a rate of 216ft3 per hour, then the rate at which the water in the pool is decreasing is in arithmetic progression. The formula for determining the nth term of an arithmetic sequence is expressed as
Tn = a + d(n - 1)
Where
a represents the first term of the sequence(initial amount of water in the pool when completely full).
d represents the common difference(rate at which it is being pumped out)
n represents the number of terms(hours) in the sequence.
From the information given,
a = 2160 degrees
d = - 216 ft3
Tn = 0(the final volume would be zero)
We want to determine the number of terms(hours) for which Tn would be zero. Therefore,
0 = 2160 - 216 (n - 1)
2160 = 216(n - 1) = 216n + 216
216n = 2160 - 216
216n = 1944
n = 1944/216
n = 9
The r% of a quantity x is computed by dividing x in 100 parts, and considering r of such parts. So, the r% of the male is
and similarly, the r% of female is
The number of males decreased by this quantity, so now it is
and the number of female increased by this quantity, so now it is
we know that these two new counts are the same number, so we can build and solve the equality
Subtract 20 and add 0.3r from both sides:
Divide both sides by 0.5 to solve for r:
Let's check the answer
The 20% of 30 is 
, while the 20% of 20 is 4. So, we are stating that 
which is true because both expressions evaluate to 24.
