Washing elephants

An experienced tamer will wash an elephant in 40 minutes. It takes a temporary worker 2 hours. How long in a minute will a tamer and a temporary worker wash three elephants together?

Final Answer:

x =  90 min

Step-by-step explanation:

$$\begin{gathered} t_1=40\text{min} \\ {t}_2=2\text{h}\to \text{min}=2\cdot 60\text{min}=120\text{min} \\ 1/t_1\cdot x+1/t_2\cdot x=3 \\ 1/40\cdot x+1/120\cdot x=3 \\ 4x=360 \\ x=\frac{360}{4}=90 \\ x=90=90\text{min} \end{gathered}$$

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