  In an asymmetric multislit interference experiment, a quanton is more likely
to pass through certain slits than some others. In such a situation one may be
able to predict which slit a quanton is more likely to go through, even without
using any path-detecting device. This allows one to talk of path
predictability. It has been shown earlier that for a two-slit interference, the
predictability and fringe visibility are constrained by the inequality
$P^2+V^2\le 1$. Generalizing this relation to the case of more than two slits
is still an unsolved problem. A new definition for predictability for
multi-slit interference is introduced. It is shown that this predictability and
quantum coherence follow a duality relation $P^2+C^2\le 1$, which saturates for
all pure states. For the case of two slits, this relation reduces to the
previously known one.
