Well, if 0.4% was defected, then 99.6% of the parts are good, because 100-0.4 is 99.6. Multiply 99.6% with 54650, and you get 54431.4. You should round down, because you can't have parts of parts. So, 54431 parts were good.
Multiples of 50 are 3000, 450, 50, and 500 and the rest are not multiples of 50
