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Re: A ladder 20 feet long is placed against a wall. If the distance on the [#permalink]
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Bunuel wrote:
A ladder 20 feet long is placed against a wall. If the distance on the ground from the wall to the ladder is 12 feet, how many feet up the wall does the ladder reach?

A. 12
B. 15
C. 16
D. 21
E. 24

Here's what's happening (the ladder is blue)


Since the wall is perpendicular to the ground we can use the Pythagorean theorem to find the value of x
We get: x² + 12² = 20²
Simplify: x² + 144 = 400
This means: x² = 256
So, x = 16
Answer: C


Alternatively, if you recall the Pythagorean triple 3-4-5, you might recognize that the two give sides of our diagram are each 4 times the values in the Pythagorean triple.
In other words 20 = 4(5), and 12 = 4(3)
So, we can conclude that x = 4(4) = 16
Answer: C
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Re: A ladder 20 feet long is placed against a wall. If the distance on the [#permalink]
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Explanation:

Ladder reach at inclination:

20^2 - 12^2 = P^2
P^2 = 400 - 144
P^2 = 256
P = 16

IMO-C
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Re: A ladder 20 feet long is placed against a wall. If the distance on the [#permalink]
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