Their income is ________________(一般家庭的3～5倍).

　　答案：three to five times that of ordinary households

　　解析：本题考查数的表达。考生要学会用"倍数+the size (length,volume) of..."，"...倍数+that of (what it was)..."的句型进行倍数的表达。Household是个集合词，表示家庭，如：average household(中等家庭);multiperson household(多人口家庭);peasant household(农户)。"家务"叫做household affairs。