Circumference 8137

One side of the rectangle is 8 cm long. When we enlarge the dimensions of this rectangle four times, we get a rectangle with a circumference of exactly 1m. How many mm does the other side of the unmagnified rectangle measure?

Correct answer:

b =  45 mm

Step-by-step explanation:

$$\begin{gathered} a=8\text{cm}\to \text{mm}=8\cdot 10\text{mm}=80\text{mm} \\ 2(4a+4b)=1000 \\ 2(4\cdot 80+4b)=1000 \\ 2\cdot (4\cdot 80+4\cdot b)=1000 \\ 8b=360 \\ b=\frac{360}{8}=45 \\ b=45=45\text{mm} \end{gathered}$$

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