In a 260-page book, the number of times the digit 5 appears in the numbering can be calculated as follows:

• 5 will occur at three places: Unit Place, Ten’s Place, Hundred’s Place.

Digit 5 in the unit's place:

• From 1 to 100: 5, 15, 25, …..85, 95:  digit 5 appears 10 times.
• From 101 to 200: 105, 115, 125, …..185, 195:  digit 5 appears 10 times.
• From 201 to 260: 205, 215, 225, 235, 245, 255:  digit 5 appears 6 times.

Digit 5 in the 10th place: 

• From 1 to 100: 50, 51, 52, 53, 54, 55, 56, 57, 58, 59: the digit 5 appears 10 times.
• From 101 to 200: 150, 151, 152, …159: the digit 5 appears 10 times.
• From 201 to 260: 250, 251, 252, …259: the digit 5 appears 10 times.

Adding all these:

• The total number of times the digit 5 appears in the numbering of a 260-page book = 10 + 10 + 6 +  10 + 10 + 10 = 56 times. 
• Therefore, the correct answer is (b) 56.