List L contains the 98 repeating decimals 0.010101..., 0.020202..., ..., 0.989898....
If each value in list L is expressed as a fraction in lowest terms, what is the sum of the denominators of all 98 fractions?
Let x = .010101....
100x = 1.010101....
99x = 1
x = 1/99
List L = 1/99, 2/99, 3/99=1/33, 4/99, 5/99, 6/99 = 2/33, 7/99, 8/99, 9/99 = 1/11, 10/99, 11/99 = 1/9, ... 98/99
If numerators are multiples of factors of 99, denominator is reduced by common factor of 99 & numerator.
99 = 3^2*11
Factors of 99 = 3, 9, 11, 33, 99
Multiples of 33 = 33, 66; Denominator = 3 in fraction in lowest terms instead of 99; Number of such terms = 2
Multiples of 11 but not 33 = 11, 22, 33, 44, 55, 66, 77, 88; Denominator = 9 in fraction in lowest terms instead of 99; Number of such terms = (88-11)/11 + 1 - 2 = 8 - 2 = 6
Multiples of 9 = 9, 18, 27, 36, 45, 54, 63, 72, 81, 90: Denominator = 11 in fraction in lowest terms instead of 99; Number of such terms = (90-9)/9 + 1 = 10
Multiples of 3 but not 9 or 33 = 3, 6, 12, 15, ...., 96; Denominator = 33 in fraction in lowest terms instead of 99; Number of such terms = (96 - 3)/3 + 1 - 10 = 32 - 10 - 2 = 20
The sum of the denominators of all 98 fractions = 99*98 - 20*(99-33) - 10*(99-11) - 6*(99-9) - 2*(99-3) = 6770
IMO C