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At a certain time of the day a tree casts a shadow 12.5 ft long. If the height of the tree is 5 ft, find the height of another tree that casts its shadow 20 ft long at the same time.

A. 6 ft
B. 8 ft
C. 10 ft
D. 11 ft​


Sagot :

B. 8 ft

Solution:

The basic proportionality theorem states that if a line is drawn parallel to one side of a triangle and it intersects the other two sides at two distinct points then it divides the two sides in the same ratio.

In the above-shown figure, DE is the height of one tree, AB is the height of another tree. AB⊥AC and DE⊥AC, therefore, AB∣∣DE

As shown in the above figure, let AB=x, CD=12.5 ft, CA=20 ft and DE=5 ft.

Using the basic proportionality theorem, we have

CD = DE

CA = AB

12.5 = 5

20 x

12.5x= 20 × 5

12.5x= 5

x = 100 = 8

12.5

Hope it helps u U^ェ^U