AbstractReflection and transmission of monoenergetical particles with a known ingoing distribution by a strongly absorbing slab is studied from the numerical standpoint.Various approximation methods based on known theoretical solutions are presented: in section III we propose an approximation based on ChandrasekharXandYfunctions; in section IV we obtain the reflection and transmission by using a variational technique, and we show that a successive-collision technique gives identical results; and in section V we propose a diffusion-like approximation, with adjusted coefficients, of the formThe first approximation gives good results for lowcvalues; the second one, for highcvalues.The diffusion-like approximation, however, is accurate to more than 2% for all values ofcbetween 0.1 and 0.9. Moreover it is far easier to compute than any of the former ones.