A can complete a work in $11\frac{1}{2}$ days. B is 25% more efficient than A and C is 50% less efficient than B. Working together A, B and C will complete the same work

4 days

A = \( { 11}_{ 2}^{ 1} \) days. 

Given,        A  :  B  :  C

                 4  :  5

 .                   :  2  :  1

Efficiency   8  : 10  :  5

⇒ Total work = 8 x \( { 11}_{ 2}^{ 1} \) = 92 units.     .(Efficiency ×Days=Total work)

⇒ Time taken by A + B + C to complete whole work = \(\frac{92}{8+10+5}\) = \(\frac{92}{23}\) = 4 days.     ..(\(\frac{Work}{Efficiency}\) = Time)