Point of taxation rule 5 for nov exam

Plz any one explan POT rules 5 [as amended throuth notification] effective from 1.4.2012.plz provide illustrations when rule 3 applies and when rule 5 if date of taxation is 1 sep 2012 in case of two situation dt of ser dt of inv dt of pay whether taxable 20:8:12 2:9:12 30:8:12 no[r ule 5] 20:8:12 10:9:12 25:8;12 no[rule 3] plz explane why in second case rule 3 applies thanks in adv