good few vs. a good few

Temat przeniesiony do archwium.
Hello!

I've got a problem with a sentence from the grammar book.

We've had good few/a good few problems with the new flat.

The book says the correct answer is 'good few'. I don't really know why. Could anyone help?
'a good few" is an idiom meaning 'several'
I don't know about 'good few'

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