AMC 10A/12A 2026 (Problem 15/10)

A pyramid of fractions starts with

\frac{1}{2}

in row 0. Each successive row has

\frac{a}{a+b}

and

\frac{b}{a+b}

; for instance, in row 1,

\frac{1}{3}

and

\frac{2}{3}

appear. In which row will

\frac{20}{27}

appear?

\text{(A)}\;5

\text{(B)}\;8

\text{(C)}\;12

\text{(D)}\;26

\text{(E)}\;\text{The node }\frac{20}{27}\text{ does not appear in the diagram.}