I
noun
BAD : The demand of butter has decreased in recent years.
GOOD : The demand for butter has decreased in recent years.
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a demand for sth (NOT of ): 'Ford has increased production to meet the demand for its new range of cars.'
II
verb
BAD : In my new job I am demanded to work overtime.
GOOD : In my new job I am required to work overtime.
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If you have to do something because of a rule, law etc, you are required to do it: 'Under the law the President is required to notify Congress when US troops face imminent hostilities.'