Coin ratio

Martin has metal coins saved up in his piggy bank: one-crown, two-crown, and five-crown coins. The ratio of crowns to five-crowns is 7:4, and five-crowns to two-crowns is 2:9. What is the ratio of crowns and double crowns?

Final Answer:

p =  7:18

Step-by-step explanation:

$$\begin{gathered} x_1:x_5=7:4 \\ {x}_5:x_2=2:9=4:18 \\ {x}_1:x_5:x_2=7:4:18 \\ p=x_1:x_2 \\ p=\frac{7}{2\cdot 9}=\frac{7}{18}\approx 0.3889=7:18 \end{gathered}$$

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