A man who is 70 inches tall has a shadow that is 80 inches long. A nearby tree casts a shadow that is 164 inches long. The shadow of the man and the shadow of the tree form similar triangles. How tall is the tree in inches?

1 answer

To find the height of the tree using the concept of similar triangles, we can set up a proportion based on the height of the man and the length of his shadow compared to the height of the tree and the length of its shadow.

Let \( h \) represent the height of the tree in inches. The relevant dimensions are as follows:

  • Height of the man: 70 inches
  • Length of the man's shadow: 80 inches
  • Length of the tree's shadow: 164 inches

Since the triangles formed by the man and the tree with their shadows are similar, we can set up the proportion:

\[ \frac{\text{Height of the man}}{\text{Length of the man's shadow}} = \frac{\text{Height of the tree}}{\text{Length of the tree's shadow}} \]

Substituting the known values into this proportion gives us:

\[ \frac{70}{80} = \frac{h}{164} \]

Next, we can cross-multiply to solve for \( h \):

\[ 70 \cdot 164 = 80 \cdot h \]

Calculating \( 70 \cdot 164 \):

\[ 70 \cdot 164 = 11480 \]

Now substituting back into the equation:

\[ 11480 = 80h \]

To isolate \( h \), divide both sides by 80:

\[ h = \frac{11480}{80} \]

Calculating \( \frac{11480}{80} \):

\[ h = 143.5 \]

Thus, the height of the tree is

\[ \boxed{143.5} \text{ inches.} \]