maths problem?

anonymous

After robbing a bank in Dodge City, the robber gallops off at 10 miles per hour. The sheriff leaves to pursue him 9 minutes later, riding at 12 miles per hour.

If the sheriff rides for t minutes, write an expression for the distance D (in miles) between the robber and the sheriff. (D(t) should be positive.)

the-truth

The sheriff rides 9 minutes later. In those nine minutes, the robber has travelled 9* (10/60) miles = 1.5 miles

From then on the relative velocity of the sherrif with respect to the robber is 2miles per hour.

So if the sherrif has travelled t minutes

then the distance between the two will be

d(t) = 1.5 - (2*t/60) miles

d(t) = 1/40 - t/30

So when t becomes 45, d(t) will be 0, ie the robber has been caught after 45 minutes.

gebobs

D = 9(t+9) - 12t = 81 - 3t

Ergo, he'll catch that scumbag in 27 minutes where D=0.