Before revision: In this situation, an assembly is critical if every released neutron has a 1 / 2.4 = 0.42 = 42 % probability of causing another fission event as opposed to either being absorbed by a non-fission capture event or escaping from the fissile core.
After revision: In this situation, an assembly is critical if every released neutron has a 1 ∕ 2.4 = 0.42 = 42 % probability of causing another fission event as opposed to either being absorbed by a non-fission capture event or escaping from the fissile core.