Bus lines

At 5.00 in the morning, four buses left the terminal at the same time. The first bus has an interval of 15 minutes, the second 20 minutes, the third 25 minutes, and the fourth 45 minutes. How many minutes will all four buses leave the terminal at the same time again?

Correct result:

t =  900 min

Solution:

$$\begin{gathered} 15=3\cdot 5 \\ 20=2^2\cdot 5 \\ 25=5^2 \\ 45=3^2\cdot 5 \\ LCM(15,20,25,45)=2^2\cdot 3^2\cdot 5^2=900 \\ t=LCM(15,20,25,45)=900\text{ min} \end{gathered}$$

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