An uncharged 4.7μF capacitor is charged to a pd of 12v through a 200 ohms resistor and then discharged through a 220 kilo-ohms resistor, calculate the time taken for the pd to fall from 12v to 3v.
I know theres the 'decay of charge' equation (with the exponential value, e) which I could use to find the time taken for volts to drop, but the textbook here hasn't even got to logarithms yet and it mentions nothing about logarithm in this whole chapter, so my hunch is that there must be another simpler way to do this question. However the page in the book does mention how to find 1% and 37% of the initial value of volts/charge, but obviously 3v from 12v is a different percentage difference.
EDIT: If there really isn't another method other than using logs, then I'm okay with that, since I get the same answer as in the back of my book. I just thought that there would be a simpler method that I've missed out, and I thought it was strange that they give absolutely no hint about logs/ln if they really are expecting me to use this method.