Turners

Two turners perform joint work in 3 hours. The first turner would perform the job himself in 7 hours. How long would the same job last for a second turner if he worked alone?

Correct result:

x =  5.25 h

Solution:

$$\begin{gathered} 3\cdot (1\mathrm{/}7+1\mathrm{/}x)=1 \\ x\mathrm{/}7+1=x\mathrm{/}3 \\ 0.190476x=1 \\ {\displaystyle \frac{4}{21}}x=1 \\ 4x=21 \\ x=21\mathrm{/}4=5.25 \\ ={\displaystyle \frac{21}{4}}\text{ h}=5.25\text{ h} \end{gathered}$$

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