A man drives from his house to the station. If he drives at the rate of 10 Km/hour, he reaches the station at 6 p.m. If he drives at 15 Km/hour, he would reach the station at 4 p.m. At what speed, in kilometers per hour, should drive so as to reach the station at 5 p.m.?

Answer 1

distance = d
say he leaves at n oclock in the afternoon
d = 10 km/hr * (6-n) hr
d = 15 km/hr * (4-n) hr
so what is n, his departure time ?
subtract
0 = 10(6-n) - 15 (4-n)
60 - 15 n = 60 - 10 n
n = 0, noon
d = 60 km
60 = v (5 - 0)
v = 12 km/hr