+17 Chad has a music addiction. Assume his collection grows exponentially. If he started by downloading 10 albums and had downloaded 96 albums after 20 months, what was his collection's average monthly growth rate?
+129962 10(1 +r)^20 = 96 divide both sides by 10
(1 + r)^20 = 9.6 take the log of both sides
log( 1 + r)^20 = log (9.6) and we can write
20* log (1 + r) = log(9.6) divide by 20 on both sides
log (1 + r) = log(9.6) / 20 and this says
10^ [ log(9.6) / 20 ] = 1 + r subtract 1 form both sides
10^[log(9.6)/ 20] - 1 = r = about 0.1197 = about 11.97% per month
