Question: At 2.30pm, David left Rose town for Lily town at a speed of 10km/h. At the same time, Muthu left Lily town for Rose town at a speed of 12km/h along the same road. If the distance between Rose town and Lily town was 6km, how far apart were the boys 15 minutes later? Answer: You have worked out how long it would take for each boy to reach the other town i.e. to cover the distance of 6 km. But the question only asks for how far they are apart after 15 min. David travels 10 km/hr. So in 15 min he travels = 10*15/60 = 2.5 km Muthu travels 12 km/hr So in 15 min he travels = 12*15/60 = 3 km Initially the boys are 6 km apart. Now since they are travelling towards each other, the distance between them has reduced by (2.5 + 3) = 5.5 km. So at the end of 15 min, the distance between them = 6 - 5.5 = 0.5 km. Hope you got it. Let me know if you need further explanations :)