To find the number of times the digit "5" appears in numbering a 260-page book, we need to count the occurrences of "5" in both the tens and units places across all page numbers from 1 to 260.

1. Units place: Pages with 5 in the units place appear once every 10 pages (e.g., 5, 15, 25, ..., 255), giving us 26 occurrences (one for each set of 10 up to 260).

2. Tens place: Pages with 5 in the tens place are from 50 to 59, 150 to 159, and 250 to 259. Each of these ranges has 10 occurrences of "5" in the tens place, resulting in 30 occurrences.

Adding both:

• 26 (units place) + 30 (tens place) = 56 times.

Answer: B. 56