The total number of digits used in numbering the pages of a book having 366 pages is

= (No. of digits in 1- digit page nos. + No. of digits in 2-digit page nos. + No. of digits in 3- digit page nos.)

= (1 x 9 + 2 x 90 + 3 x 267) = (9 + 180 + 801) = 990.