(1) This burglar alarm won’t work unless we are lucky or the burglar uses the front door.(2) We can’t count on being lucky.(3) We can’t count on the burglar using the front door.(4) We can’t count on a burglar alarm that won’t work.______________________∴(5) We can’t count on this burglar alarm. (from 1-3)(6) This burglar alarm is the only one that we have.(7) We need a burglar alarm that we can count on.______________________∴(8) We need a new burglar alarm. (from 1)

(1) We are not lucky. (2) The burglar won’t use the front door. ______________________ ∴ (3) This burglar alarm won’t work. (from 1-2) (4) We need a burglar alarm that will work. ______________________ ∴ (5) We need a new burglar alarm. (from 3-4)

(1) We can’t count on this burglar alarm. ______________________ ∴ (2) It won’t work unless we are lucky. (from 1) (3) We can’t count on this burglar alarm. ______________________ ∴ (4) We need a new alarm. (from 3)