You can select 7 manufactures from 11 manufactures by   ways =  = 330 ways.


It is your sample space, or space of events.


How many of them contain exactly 2 good of the best 3?


First, you can select 2 good manufactures from the best 3 by 3 ways.


Second, you can complement these 2 manufactures to 7 by adding 5 manufactures from 11-3 = 8 remaining manufactures,

and you can do it by   ways =  = 56 ways.


Thus 3*56 is the number of favorable choices.


Then the probability under the question is   = 0.5091 = 50.91%.    ANSWER