# Two buses

The first bus runs 15 minutes the second bus runs after 21 minutes. Together they both leave at 7:00 on Monday. When and what day will they meet?

Result

t = 8:45 hh:mm

#### Solution:

$15=3 \cdot 5 \ \\ 21=3 \cdot 7 \ \\ LCM(15, 21)=3 \cdot 5 \cdot 7=105 \ \\ \ \\ t_{1}=LCM(15,21)=105 \ \text{min} \ \\ t_{2}=t_{1} \rightarrow h=t_{1} / 60 \ h=105 / 60 \ h=1.75 \ h \ \\ \ \\ t=7.00 + t_{2}=7.00 + 1.75=\dfrac{ 35 }{ 4 }=8.75=8:45 \ \text{hh}:\text{mm}$

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