A can do a piece of work alonein 8 days. B can do the same work alone in 21 days. If they work together for 3 days, then how much work is completed?

$\frac{29}{67}$ $\frac{31}{65}$ $\frac{27}{64}$ $\frac{29}{56}$

$\frac{29}{56}$

A = 8 days, B = 21 days,   ⇒ A + B worked for 3 days = (21 + 8) x 3 = 29 x 3 = 87 units,  ..(Efficiency × Days = Work) ⇒ The part of total work they completed in 3 days is = \(\frac{87}{168}\) = \(\frac{29}{56}\).