Hi, Can the following be factorise'd further? 16abc + 24abc - 4ac <-- I think that "c" in that second term is incorrect 4a ( 4bc + 6b -c ) - Should I be factoring 4bc + 6b - c further ? No you can't factor it further. 16ab - 16as - 24pt + 24ps 16a(b-s) - 24p(t-s) - Should I be factoring this further ? That is not factored at all. To be factored there must be no plus or minus signs outside of parentheses. All you can do with 16ab - 16as - 24pt + 24ps is factor out an 8 8(2ab - 2as - 3pt + 3ps) Edwin