Henry is a hitchhiking. He gets a ride with a trucker who's just leaving Fredsville with a delivery. Henry soon notices that they pass a returning delivery truck every ten minutes on the dot. All the delivery trucks, including the one Henry is riding in, travel the same speed. "How many trucks, arrive at the city every hour? Henry asked. "Well, obviously 6," says the trucker, "since 60/10 = 6." Henry is skeptical. Answer Henry's question correctly. HELP ME PLEASE

Hint: consider that the relative speed of the trucks approaching Henry is twice as fast as the speed of the trucks approaching their destination. Now - care to hazard a guess as the frequency of trucks arriving at their destination?

But it says they are going the same speed. My guess is there is 12 because 6 would be coming in and 6 would be coming out.

That is not a answer to the question. The question asks at what frequency, in trucks/hr, do trucks enter the city. This is based upon your truck heading away from the city at the same speed as the trucks are heading towards the city.

Forget the other trucks for a moment, Imagine that you're travelling 60km/h (I;m canadian, deal with it.), there are signs every 10 km. You will see 6 in a hour, one every 10 minutes. These aren't moving. Imagine that you are now moving 120 km/h. You will see twice as many signs, 12, one every 5 minutes. They're still 10km apart. Now imagine that the signs are on trucks moving towards you. If you're going 60 km/h and they're going 60km/h, the relative speed between the two is still 120km/h. You will still pass 12 sign trucks, one ever 5 minutes. Now the sign trucks are still 10 km apart, traveling at that speed they're leaving 10 min apart, but you're see them every 5 minutes.

Consider this, do you wish to revise your answer?

Ohhh! Okay, I get it now. Thank you so much!