"A number of" and "a great deal of"

[ngoc_lan]

Are there any differences between "a number of" and "a great deal of"?
If I say: "He visited ______ countries", which word is correct?
Thanks for your help.

[Rover_KE]

They are not used in the same way.

'He visited a number of countries' (maybe three or four).

'He visited a great number of (or 'a great many') countries' (about 15 to 20).

'His alcoholism caused his family a great deal of hardship'.

'Passing my driving test gave me a great deal of pleasure'.

Rover

[ngoc_lan]

Thank you very much

[philo2009]

In other words, 'a number of' + PLURAL noun, 'a great deal of ' + SINGULAR NONCOUNT noun.