Summer tires

Three tire servants have to change the summer tires on 6 cars in 2 hours. Mark's replacement would take 4.5 hours, Jirka would do it in 3 hours and 10 minutes, and Honza in 4 hours. Will they be able to replace all tires at the desired time?

Correct result:

t =  1.269 h

Solution:

$$\begin{gathered} t={\displaystyle \frac{1}{{\displaystyle \frac{1}{4.5}}+{\displaystyle \frac{1}{3+10\mathrm{/}60}}+{\displaystyle \frac{1}{4}}}}={\displaystyle \frac{684}{539}}\doteq 1.269=1.269\text{ h } \\ t<2 \end{gathered}$$

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