Apple harvest

A father would pick all the apples on his own in 8 days. After he had worked alone for 2 days, his son joined him, and they finished the remaining picking together in 4 more days. How long would it take the son to pick all the apples on his own?

Final Answer:

s =  16

Step-by-step explanation:

$$\begin{gathered} o=8 \\ \frac{1}{o}\cdot 2+4\cdot (\frac{1}{o}+\frac{1}{s})=1 \\ s\cdot \frac{2}{o}+4\cdot (\frac{s}{o}+1)=s \\ 2\cdot s/o+4\cdot s/o+4=s \\ 2\cdot s/8+4\cdot s/8+4=s \\ 2s=32 \\ s=\frac{32}{2}=16 \\ s=16 \end{gathered}$$

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