There's a problem I've been asked to do sans calculator (though I don't think it requires one) that I'm having a little bit of trouble with for some reason. The question goes as follows:

A motorcyclist is stopped at a checkpoint for 24 minutes. Upon leaving the checkpoint he increases his constant speed by 10km/h. After traveling an additional 80km he's eliminated the delay caused by the checkpoint. What was the motorcyclist's speed when he arrived at the checkpoint? (a.k.a. before the 10km/h speed increase).

I've made a bit of headway solving it but I keep hitting dead ends... it feels like something's missing. Help would be appreciated. Thanks very much :)

Guest Jul 17, 2014