Christian made 1000 pancakes.
Explanation:
Let us represent the total amount of Pancake made by Christian as = K
From the problem;
Christian ate 
of the pancake in the morning = * K = K
We know that Christian cannot eat her pancake and at the same time have it, the remaining pancake will then be:
total amount of cake - fraction eaten
Remainder = K - K= 
K
In the afternoon, we know that she ate 1/4 of the remaining cake:
K* K = 
K
The remaining cake in the afternoon will be:
Total amount of cake remaining from morning - amount eaten in the afternoon
= K - K
= 
K
The fraction of the cake remaining in the afternoon is K
Since she had 300cakes left in the afternoon, then :
K= 300
K = 1000 pancakes
Therefore Christian made 1000 pancakes.
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The frequency of the human ear canal is 2.92 kHz.
Explanation:
As the ear canal is like a tube with open at one end, the wavelength of sound passing through this tube will propagate 4 times its length of the tube. So wavelength of the sound wave will be equal to four times the length of the tube. Then the frequency can be easily determined by finding the ratio of velocity of sound to wavelength. As the velocity of sound is given as 339 m/s, then the wavelength of the sound wave propagating through the ear canal is
Wavelength=4*Length of the ear canal
As length of the ear canal is given as 2.9 cm, it should be converted into meter as follows:
Then the frequency is determined as
f=c/λ=339/0.116=2922 Hz=2.92 kHz.
So, the frequency of the human ear canal is 2.92 kHz.
Let height of twin falls = x
height of seven falls = 2.5x
x + 2.5x = 420
3.5x = 420
x = 420/3.5 = 120
so twin falls = x = 120 ft
seven falls = 2.5x = 300 ft
Friction stole the book's kinetic energy, and turned it into heat energy ... which blew away in the breeze.
