Complex sentence: Western Australia's population in 1850 was approximately 5000 individuals, and with ongoing free settler arrivals during the convict period, the state's population increased approximately five-fold in less than 20 years.
Split into simpler sentences: Western Australia's population in 1850 was approximately 5000 individuals. With ongoing free settler arrivals during the convict period, the state's population increased approximately five-fold in less than 20 years.