Thread:RePeat/@comment-1693968-20140305220535/@comment-1693968-20140307132031

Obi the LEGO Fan wrote: RePeat wrote: The brigantine was sailing at full speed. He was 30 miles at sea when Lord Nelson began to give chase at twice the speed of the brigantine. If Lord Nelson caught up in six hours, what was the brigantine's speed? The answer is five mph. I actually answered the question in chat, but then realized you had left like right before I typed the answer.

You have to create a variable for what you want to solve for. In this case that is the speed of the brigantine, so we make that speed equal X. Lord Nelson's speed is 2x. Now, we know that the brigantine has a 30 mile head start, and that it took six hours for the two ships to be at the same place. So we set up the equation 6(2x) = 6x + 30 or 12x = 6x + 30, which simplifies to 6x=30, x = 5. To explain the problem: in six hours the brigantine will have gone (5•6)+30 or 60 miles, which is the same Lord Nelson would do, since he went 10 mph for six hours. You could either go through all that, or you could notice that it simplifies to Lord Nelson having to travel 30 miles in 6 hours going x speed.