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Did You Find Out? Get the Answer to the Riddle of E-News Issue No. 05, September 2014

How deep is the pond?

riddle, e-news 2014-5, brain teaser, water lily, pond, challenge, newsletter
Can you figure out how deep the pond is?

A park contains a large pond whose surface is covered by countless water lilies. One of them is exactly 10 cm above the pond’s water level. Suddenly, a strong wind begins to blow and the water lilies drift away slightly. The lily, which towered 10 cm above the pond`s surface, is now located 60 cm away from its original position directly on the water.

How deep is the pond?


Solution

Calculate the depth of the pond with the help of  the Pythagoras Theorem!
Calculate the depth of the pond with the help of the Pythagoras Theorem!

Without any wind, the water lily is perpendicular to the ground of the pond and its water surface. Due to the strong wind, the water lily is pushed to the sides and consequently, its stem completely disappears under the water's surface. According to the Pythagoras Theorem, the depth of the pond can be calculated as follows:

x2 + 602 = (x + 10)2
x2 + 3600 = x2 + 20x + 100
20x = 3500
x = 175 (cm)

The pond is 1.75 m deep.