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:

$3 \cdot \ (1/7 + 1/x)=1 \ \\ x/7 + 1=x/3 \ \\ 0.190476x=1 \ \\ \dfrac{ 4 }{ 21 }x=1 \ \\ 4x=21 \ \\ x=21 / 4=5.25 \ \\ =\dfrac{ 21 }{ 4 }=5.25 \ \text{h}$

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