Choose the correct alternatives from given ones that will complete the series. 321,301,?,181,21

The pattern is subtract 20 then subtract 40 alternately: 321-20=301, 301-40=261, 261-20=241, 241-40=201... but wait, that gives 201 not 181. Let me recalculate. Actually checking: 321-20=301, then to get 181 at position 5, we need: position 3 should be such that subtracting something gives 181. If it's -20, -40, -20, -40: 321-20=301, 301-40=261, 261-20=241, 241-40=201. But we have 181, not 201. The given answer says 261, which would fit position 3. But then position 4 would be 261-20=241, and position 5 would be 241-40=201, not 21. Wait, the last term is 21, not 181. Reading again: 321,301,?,181,21. So we have: 321→301 is -20. To go from 181 to 21 would need -160. Let me check if 261 fits: 321-20=301, 301-40=261, 261-80=181, 181-160=21. The pattern is subtract 20, 40, 80, 160 (doubling each time). So 261 is correct.