Quote Originally Posted by mmmichel

Note that JohnnyWalker was correct and that his method is equivalent. In his example, TO = 20sec, LO = 4in, LN = 8in therefore TN = 20*2^2 or 80 seconds, which is 4 times the original time. This is, of course, because (LN/LO)^2 = LN^2/LO^2.
Just to be clear on precedence of operations for the sake of those like me, who are 30 years past algebra classes or otherwise out of practice:

TN = 20*(2^2) or 80 seconds, which is correct

(as opposed to TN = (20*2)^2 or 1600 seconds, which is incorrect.)