math
posted by wan .
if i drive home with a speed of 60km/h,I will arrive an hour ealier than expected.If i drive 40km/h then i will arrive an hour later than expected.At what speed should i travel in order to arrive BANG on time?

time to go home at 40 km/h  d/40 hours
time to go home at 60 km/h  d/60 hours
d/40  d/60 = 2 (there is a 2 hr difference in the two times)
time 120
3d  2d = 240
d = 240
so the two times are 240/40 and 240/60
or 6 and 4 hours,
so he wants to take 5 hours
speed = 240/5 = 48 km/h