Height of the woman = 5 ft
Rate at which the woman is walking = 7.5 ft/sec
Let us assume the length of the shadow = s
Le us assume the <span>distance of the woman's feet from the base of the streetlight = x
</span>Then
s/5 = (s + x)/12
12s = 5s + 5x
7s = 5x
s = (5/7)x
Now let us differentiate with respect to t
ds/dt = (5/7)(dx/dt)
We already know that dx/dt = 7/2 ft/sec
Then
ds/dt = (5/7) * (7/2)
= (5/2)
= 2.5 ft/sec
From the above deduction, it can be easily concluded that the rate at which the tip of her shadow is moving is 2.5 ft/sec.
B. Between 20 and 25 minuets
Brooke's speed is decreasing between 20 and 25 minutes. According to the graph Brooke's speed is decreasing during that time period.
There are 
ways of drawing a 4-card hand, where
is the so-called binomial coefficient.
There are 13 different card values, of which we want the hand to represent 4 values, so there are 
ways of meeting this requirement.
For each card value, there are 4 choices of suit, of which we only pick 1, so there are 
ways of picking a card of any given value. We draw 4 cards from the deck, so there are 
possible hands in which each card has a different value.
Then there are 
total hands in which all 4 cards have distinct values, and the probability of drawing such a hand is
C = pi * r ^squared
r = is radius
square the radius, multiple by r
or
2 x pi x r
20t +15t+90+25t-75=60t+15
60t+15/3=20t+5 as the average
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