Two workers

One worker needs 40 hours to do a job, and the second would do it in 30 hours. They worked together for several hours, then the second was recalled, and the first completed the job itself in 5 hours. How many hours did they work together, and how much did each of them do?

Correct result:

x =  15 h
a =  0.5
b =  0.5

Solution:

$$\begin{gathered} x\cdot (1\mathrm{/}40+1\mathrm{/}30)+5\mathrm{/}40=1 \\ 7x=105 \\ x=15=15\text{ h} \end{gathered}$$

$a={\displaystyle \frac{x+5}{40}}={\displaystyle \frac{15+5}{40}}={\displaystyle \frac{1}{2}}=0.5$

$b={\displaystyle \frac{x}{30}}={\displaystyle \frac{15}{30}}={\displaystyle \frac{1}{2}}=0.5$

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