A can do a piece of work alone in 30 days. B is 25% less efficient than A, while C is $33\frac{1}{3}$% more efficient than B. In how many days can A, B and C, working together, complete the work?

$\frac{120}{11}$ days

A = 30 days, 

B is 25% less efficient than A, while C is 33.33% more efficient than B, therefore,

A : B : C = 4 : 3 : 4  (Efficiency)

⇒ Total work = 4 x 30 = 120 units,   ..(Efficiency × Days = Total work)

⇒ Time required for A + B + C to complete the work = \(\frac{120}{4+3+4}\) = \(\frac{120}{11}\) days  ..(\(\frac{Work}{Efficiency}\) = Time)