What are the steps to solve for n?:
50000 = 1000(1 + 0.8)^n
divide both sides by 1000
(1.08)^n = 50
take log of both sides
log (1.08^n) = log 50
n log 1.08 = log 50
n = log50/log1.08 = 50.8312 = appr 50.8
check:
1000(1.08)^50.8312 = 49999.95 , not bad eh?