Permutation - Two couple at the round table question

Two couples want to sit next to each other separately.

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[yingshiantay]

hi sir, for question b) is it mean that the two couple must sit seperately?
if for 480 ways, then it include the two couples to sit seperately and next to each other right?
so to get the number of ways the two couples want to sit seperately, is it need to minus 192 ways, like 480 - 192 = 288 ways? am i right?
hope for explaination, tq

[kahloktai]

Why the round table formula must minus 1?