There are 4 possibilities:

no crit, no crit
CRIT, no crit
no crit, CRIT
CRIT, CRIT

2nd sentence says that there must be at least one crit, so "no crit, no crit" is removed, leaving:

CRIT, no crit
no crit, CRIT
CRIT, CRIT

Equal odds for each, therefore: 

1 in 3, or 1/3