Amazon river length

The longest Brazilian river, the Amazon, is ten times longer than the two Czech rivers, Vltava and Berounka. The ratio of the lengths of the Vltava and Berounka is 9:5. At the same time, the length ratio of the Vltava and Morava rivers is 5:4. How many kilometers does the Amazon flow if we know that Moravia is 360 km long?

Final Answer:

a =  7000 km

Step-by-step explanation:

$$\begin{gathered} m=360\text{km} \\ v:b=9:5 \\ v:m=5:4 \\ v=m\cdot \frac{5}{4}=360\cdot \frac{5}{4}=\frac{360\cdot 5}{4}=\frac{1800}{4}=450\text{km} \\ b=v\cdot \frac{5}{9}=450\cdot \frac{5}{9}=\frac{450\cdot 5}{9}=\frac{2250}{9}=250\text{km} \\ a=10\cdot (v+b)=10\cdot (450+250)=7000\text{km} \end{gathered}$$

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