A factory produces two types of electric lamps A and B, in an experiment relating their life, the following results were obtained:

 

Length of life in 1000 hours	4-6	6-8	8-10	10-12
Number of lamps A	7	9	11	3
Number of lamps B	5	10	13	2

State (i) which model has a longer average life?
(ii) Which model is more consistent in terms of life?