J can complete a work in 21 days, K can complete it in 42 days and L can complete it in 63 days. If J, K and L work together, in how many days can they complete the work?

$11 \frac{5}{11}$

J = 21 days, K = 42 days, L = 63 days,

⇒ Time required for J + K + L to complete the work = \(\frac{126}{6+3+2}\) =  \(\frac{126}{11}\) = \( { 11}_{11 }^{5 } \) days,      ..(\(\frac{Work}{Efficiency}\) = Time)