A can do piece of work in 15 days. B is 25% more efficient than A, and C is 40% more efficient than B, A and C work together for 3 days and then C leaves. A and B together will complete the remaining work in:

Solution (By Examveda Team)

\[\begin{array}{*{20}{c}} {}&\begin{gathered} {\text{A}}\,\,\,\,\,\,{\text{B}}\,\,\,\,\,\,{\text{C}} \hfill \\ {\text{4}}\,\,\,{\text{:}}\,\,\,{\text{5}}\,\,\,{\text{:}}\,\,\,{\text{7}} \hfill \\ {\text{5}}\,\,\,{\text{:}}\,\,\,{\text{7}}\,\,\,\,\,\,\,\,\,\, \hfill \\ \end{gathered} \\ {{\text{Efficiency}} \to }&{\overline {\,4\,:\,5\,:\,7\,} } \end{array}\]
Total work = 4 × 15 = 60 units
(A + C) × 3 + (A + B)x = 60
11 × 3 + 9 × x = 60
33 + 9x = 60
9x = 27
x = 3 days