Trains to portadown leave a train station every 14 minutes
trains to portrush leave a train station every 20 minutes
a train to portdown and a train to portrush both leave the station at 8am
when will a train to portdown and a train to portrush both leave the train station at the same time

We need to find the lowest common multiple...

multiples of 14 are : 14,28,42,56,70,84,98,112,126,140,154
multiples of 20 are : 20,40,60,80,100,120,140

so the lowest common multiple is 140so thats 140 minutes= 2 hrs 20 minutesfrom 8:00 = 10:20

so they will both leave at the same time of  10:20 a.m. <==