What percentage

Petra made lemonade from one litre of 100% fruit juice and three litres of water. When she tasted it, she found it was too sweet and would not suit everyone. She kept two litres for her friends and added two more litres of water to the remaining two litres.
What percentage of the drink did her friends drink, and what percentage did the others drink?

Final Answer:

p₁ =  25 %
p₂ =  12.5 %

Step-by-step explanation:

$$\begin{gathered} S=1\text{l} \\ V=3\text{l} \\ {p}_1=100\cdot \frac{S}{S+V}=100\cdot \frac{1}{1+3}=25\% \end{gathered}$$

$$\begin{gathered} V_2=2\text{l} \\ {p}_2=100\cdot \frac{S/2}{(S+V)/2+V_2}=100\cdot \frac{1/2}{(1+3)/2+2}=\frac{25}{2}\%=12.5\% \end{gathered}$$

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