Respuesta :
Is the question - did they mistakenly say "dollar" rather than "years?"
x = # of years
10,000 = 20,000 (0.85)^x, first divide both sides by 20,000
0.5 = (0.85)^x, next take the ln of both sides
ln 0.5 = ln (0.85)^x, by rules of logarithms you may move x to make it a coefficient of the logarithm
ln 0.5 = x (ln 0.85), divide both sides by ln (0.85)
x = (ln 0.5)/ (ln 0.85) = (-0.693)/(-0.1625) = 4.26 years
x = # of years
10,000 = 20,000 (0.85)^x, first divide both sides by 20,000
0.5 = (0.85)^x, next take the ln of both sides
ln 0.5 = ln (0.85)^x, by rules of logarithms you may move x to make it a coefficient of the logarithm
ln 0.5 = x (ln 0.85), divide both sides by ln (0.85)
x = (ln 0.5)/ (ln 0.85) = (-0.693)/(-0.1625) = 4.26 years
