## Related Rates

**Problem**

While this problem looks straight from a differential calculus textbook, it requires no advanced math.

Two bugs sit on either side of a bubble. The radius *r* of the bubble is expanding with *dr/dt*=3 cm/s. The distance between the bugs is *d* and they sit on either side of a 60 degree arc, find *dd/dt* when *r*=2.

**Solution**

Since the arc is 60 degrees, then d=r and thus dd/dt=dr/dt, dd/dt=2 at all times.

**If you have a tricky or interesting problem that you’d like to see on Problem Of The Week, email one of our Expert Tutors!**