Three painters

The three painters have painted bridges. The first would work done in 5 days, the second in 6 days, and the third in 7.5 days. How long will the bridge work if they work together?

Final Answer:

x =  2 d

Step-by-step explanation:

$$\begin{gathered} d_1=\frac{1}{5}+\frac{1}{6}+\frac{1}{7.5}=\frac{1}{2}=0.5 \\ x=\frac{1}{d_1}=\frac{1}{\frac{1}{2}}=2\text{d} \end{gathered}$$

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