If all the numbers from 501 to 700 are written, what is the total number of times the digit 6 appears ?

Answer: Option C

Numbers from 501 to 599 which have 6 as digit are 506, 516, 526, 536, 546, 556, 560, 561, 562, 563, 564, 565, 566, 567. 568, 569, 576, 586 and 596, i.e., 6 occurs 20 times.
Number of times 6 occurs from 600 to 699 = 100 + 20 = 120
∴ Total number of times 6 occurs = 20 + 120 = 140