Question

In a typing class, the average number of words per minute N typed after t weeks of lessons was found to be N= 154/(1+ 6.4e^-.2t). Find the time necessary to type 65 words per minute.

Answer 1

\[65=\frac{154}{1+ 6.4e^{-.2t}}\] is a start

Answer 2

ok thanks but what do i do next

Answer 3

i would start by writing
\[1+6.4e^{-.2t}=\frac{154}{65}\]

Answer 4

wait so you multiplied 1+6.4e^-.2e and then divided by 65?

Answer 5

yes

Answer 6

ok

Answer 7

\(a=\frac{b}{c}\iff c=\frac{b}{a}\)

Answer 8

then subtract 1 from both sides

Answer 9

got it

Answer 10

you should get
\[e^{-.2t}=\frac{89}{65}\] if my arithmetic is right

Answer 11

ok

Answer 12

wait what happened to the 6.4 did you divide?

Answer 13

i still don't fully understand but thank you for your help

Answer 14

oh damn hold on

Answer 15

\[e^{-.2t}=\frac{89}{65}\] is a mistake
sorry

Answer 16

should be \(6.4e^{-2t}=\frac{89}{65}\)

Answer 17

so you next have to divide by \(6.4\)

Answer 18

ok

Answer 19

numbers get real ugly, time to revert to decimals

Answer 20

maybe
\[e^{-.2t}=.235577\]

Answer 21

then write in logarithmic form as\[-.2t=\ln(.23557)\] and finally divide by \(-.2\)
use a calculator

Answer 22

check my arithmetic, it is not perfect

Answer 23

ok and thanks again :)