A and B together can finish a work in 20 days. If they worked together for 8 days, then what was the share of work that was yet to be completed?

$\frac{3}{5}$

A + B = 20 days,

Lets' take efficiency of A + B as 1.

Therefore, total work = 1 x 20 = 20 units,   ..(Efficiency × Days = Total work)

⇒ A + B worked for 8 days = 1 x 8 = 8 units,

⇒ Fraction of work left = \(\frac{20 - 8}{20}\) = \(\frac{12}{20}\) = \(\frac{3}{5}\)