A shipment of TV sets, some weighting 30kg each and the others weighing 50kg each, has a total weight of 880kg. if there are 20 tv sets all together, how many weigh 50kg?
Let's say the number of TV sets weighing 30kg each is x.
The number of TV sets weighing 50kg each is then 20 - x.
The total weight of the TV sets weighing 30kg each is 30x.
The total weight of the TV sets weighing 50kg each is 50(20 - x).
The total weight of all TV sets is 30x + 50(20 - x) = 880kg.
Expanding the equation gives 30x + 1000 - 50x = 880.
Combining like terms gives -20x + 1000 = 880.
Subtracting 1000 from both sides gives -20x = -120.
Dividing both sides by -20 gives x = 6.
Therefore, the number of TV sets weighing 50kg each is 20 - 6 = <<20-6=14>>14. Answer: \boxed{14}.