Question 1861
this is fairly easy to be honest, just don't freak out at converting the english to maths...just take it steady...

Let r = speed of robber = 80mph

Using {{{speed = distance/time}}}, we get 80 = d/t....equation1

Let p = speed of police = 90mph. And note they start 30 minutes later (or 1/2 hours later!!!!!).

so, for the police to arrive at the same point (d miles), we have 90 = {{{d/(t-(1/2))}}} equation2

Substitute equn1 into 2 for d ie d=80t. So equation2 is now

{{{90 = (80t)/(t-(1/2))}}}

{{{90(t-(1/2)) = (80t)}}}
{{{90t - 45 = 80t}}}
{{{10t = 45}}}
therefore t = 4.5 hours.

Hence, as d=80t, d=360miles.


cheers
Jon.