At 9: 00 am andrew left exeter for portsmouth, cycling at 12 miles per hour. at 10: 00 am stacy left portsmouth for exeter, cycling at 16 miles per hour. the distance from exeter to portsmouth is 20 miles. find the time when they met.

Andrew - 12 miles an hour to cover 20 miles - 1 and 2/5 hours - 1hr 24 mins
Arrives in Portsmouth at 10:24.

Stacy - 16 miles an hour to cover 20 miles - 1 and 1/5 hours - 1hr 12 mins
Arrives in Exeter at 11:12.

Stacy is always moving 12 minutes faster than Andrew. When Stacy leaves, Andrew is 8 miles from Portsmouth, which will take him 24 minutes to complete. Stacy will do 8 miles in 12 minutes, but by this time Andrew has cycled forward 4 miles (8 miles = 24 mins, 4 miles = 12 minutes), so Stacy would have met Andrew 6 minutes beforehand (8 miles = 12 mins, 4 miles = 6 mins) which makes the time - 

1 hr + 12 mins - 6 mins = 11:06.

I apologise if this is wrong, my teacher was ill when we covered this subject.