S = d/t
st = d
t = d/s
The time going is t1.
The time returning is t2.
The total time is 4 hours, so we have t1 + t2 = 4
The speed of the current is c.
The speed going is 9 + c.
The speed returning is 9 - c.
t1 = 16/(9 + c)
t2 = 16/(9 - c)
t1 + t2 = 16/(9 + c) + 16/(9 - c)
4 = 16/(9 - c) + 16/(9 + c)
1 = 4/(9 - c) + 4/(9 + c)
(9 + c)(9 - c) = 4(9 - c) + 4(9 + c)
81 - c^2 = 36 - 4c + 36 + 4c
81 - c^2 = 72
c^2 = 9
c^2 - 9 = 0
(c + 3)(c - 3) = 0
c + 3 = 0 or c - 3 = 0
c = -3 or c = 3
We discard the negative answer, and we get c = 3.
The speed of the current is 3 mph.
Use the quadratic formula, the second, the 6th answers are correct.
Answer:

Step-by-step explanation:
we have

where
W is the weight in pounds
x is the number of training cycles completed
For 
substitute the value of x in the function

Answer:

Step-by-step explanation:
Given
Represent radius with r and height with h


when 
Express radius in terms of height



First, we need to determine the volume of the cone in terms of height.

Substitute 




Differentiate both sides w.r.t time (t)


Solve for 

At this point,
and 
So, we have:




Hence:
The rate is 
I don't know, what did the policeman shout to the math professor as a mob of excited calculus students crowded around these displays on his graphing calculator?