The "learning curve" describes the rate at which a person learns certain tasks. If a person sets a goal of typing N words per minute (wpm), the length of time t (in days) to achieve this goal is given by the following formula. t=62.5ln(1-N/80)

Question

(a) According to this formula, what is the maximum number of words per minute?

(b) Solve for N.

.

Answer 1

ln(x) is only defined for x>0, so 1-N/80 > 0
That is, N<80

The problem here is that 1-N/80 < 1, so ln(1-N/80) is negative. But, t must be positive.

Typo?