# Similarity and Ratios ## Step-by-step guide: $\checkmark$ Two or more figures are similar if the corresponding angles are equal, and the corresponding sides are in proportion. ## Examples: 1) A girl 160 cm tall, stands 360 cm from a lamp post at night. Her shadow from the light is 90 cm long. How high is the lamp post? Write the proportion and solve for missing side. $\frac{\text { Smaller triangle height }}{\text { Smaller triangle base }}=\frac{\text { Bigger triangle height }}{\text { Bigger triangle base }}$ $\Rightarrow \frac{90 \mathrm{~cm}}{160 \mathrm{~cm}}=\frac{90 + 360 \mathrm{~cm}}{x} \Rightarrow 90 x= 160 \times 450 \Rightarrow x= 800 \mathrm{~cm}$ 2) A tree 32 feet tall casts a shadow 12 feet long. Jack is 6 feet tall. How long is Jack's shadow? Write a proportion and solve for the missing number. $\frac{32}{12}=\frac{6}{x} \rightarrow 32 x= 6 \times 12 = 72$ $32 x= 72 \rightarrow x=\frac{72}{32}= 2.25$ feet
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Answer

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Step 1
: Write down the given information and the proportion for the problem.

\frac{\text{Bigger triangle height}}{\text{Bigger triangle base}} = \frac{\text{Smaller triangle height}}{\text{Smaller triangle base}}
The given information is: - The height of the tree (bigger triangle) is 32 feet. - The length of the tree's shadow (base of the bigger triangle) is 12 feet. - Jack's height (smaller triangle) is 6 feet. - We need to find the length of Jack's shadow (x, the base of the smaller triangle). The proportion is:

Step 2
: Plug the given values into the proportion and solve for the unknown.

x = \frac{6 \times 12}{32} = \frac{72}{32} = 2.25~\text{feet}
Cross-multiply to solve for x: Divide both sides by 32:

Final Answer

Jack's shadow is 2.25 feet long.