MATH
posted by NICK .
THANKS FOR THE ANSWER
BUT I DON'T KNOW HOW TO WRITE THE PROBLEM
TO ARRIVE TO THAT ANSWER

I assume you mean the Santa page numbers?
no. of 1digit pages = 9
no. of 2digit pages = 90
so,
1*9 + 2*90 + 3n = 690
3n = 501
n = 167
9+90+167 = 266
Hmmm. I don't get 245. Check my math.