Answer: 20 feet
Step-by-step explanation:
This represents a right angled triangle with the length of the slide being the hypotenuse, the height of the ladder being the height of the triangle and the distance from the base of the ladder being the length.
Solve with Pythagoras rule:
c² = a² + b²
c = hypotenuse
a= length
b = height
29² = 21² + b²
841 = 441 + b²
b² = 841 - 441
b² = 400
b = √400
b = 20 feet
We can expand the logarithm of a product as a sum of logarithms:
Then using the change of base formula, we can derive the relationship
This immediately tells us that
Notice that none of 
can be equal to 1. This is because
for any choice of 
. This means we can safely do the following without worrying about division by 0.
so that
Similarly,
so that
So we end up with
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Another way to do this:
Then
So we have
If a question has four possible answers, and you are strictly guessing regarding which of them is correct, then the chances of your choosing the correct one from the four is 1 in 4, or 0.25.
