.
n + (n+1) = 479
2n = 479 - 1 = 478
n = 478/2 = 239.
Formal answer is 239 for the left page and 240 for the right page.
But if you open any book, which has traditional numeration, you will NEVER see such pair of pages.
In traditional numeration, left page has even number, while the right page has odd number.
It is typical case when the author of the problem DOES NOT know the subject or/and even do not think about it . . .
I just posted such notices MANY TIMES at this forum in similar situations, when similar problems with similar defects came.
Be aware (!)