Complex sentence: It was estimated that when Raffles arrived in Singapore in January 1819, Singapore had about 120 Malays, 30 Chinese and some local tribes (the Orang Laut), and by 1821, the population was estimated to have increased to 4,724 Malays and 1,150 Chinese.
Split into simpler sentences: It was estimated that when Raffles arrived in Singapore in January 1819, Singapore had about 120 Malays, 30 Chinese and some local tribes (the Orang Laut). By 1821, the population was estimated to have increased to 4,724 Malays and 1,150 Chinese.