表示增加多少或减少多少用by。
The number of students in our university has increased by 20 percent over the previous year.
我们大学的学生数量比上一年增加了百分之二十。
The output of coal went up by four times.
煤炭产量增加了四倍。
The production has multiplied by five times.
产量增加了五倍。
The saled of washing machines have increased by a factor of nine.
洗衣机的销售量增加了9倍。
The production was reduced by thirty percent.
生产减少了百分之三十。
The cost of air-conditioners has decreased by 50 percent.
空调的成本下降了50%。
表示增加到/至……或减少到/下降到/至……用介词to。
The students in our university have increased to 12,000.
我们大学的学生已增加到一万二千。
The production was reduced to thirty percent.
生产减少到百分之三十。
注意区分下列句型：
increased by 30% 增加了30%
increased to 3,000 增加到3,000
increase 3 times/threefold 增加至三倍 或 增加了两倍
increase by 3 times 增加了三倍
3 times as long as 为……的三倍长，或比……长二倍
3 times longer than 为……的四倍长，或比……长三倍
decrease by 30% 减少了30%
decrease to 30% 减少至30%
The students in our university have increased ___ 12,000.
A. by B. on C. to D. up
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