You’d have to list (there could also be a PnC approach but for such a small number it would end up being 3 times as long and 10 times as complicated). I am assuming all sides to be natural numbers (ideally should be specified in the question…otherwise answer would be infinity)
No side can be 10 or more. So start with 9:
9 8 3
9 7 4
9 6 5
8 7 5
Hence 4 such triangles I think.

how many scalene triangles are possible with perimetre 20?

You’d have to list (there could also be a PnC approach but for such a small number it would end up being 3 times as long and 10 times as complicated). I am assuming all sides to be natural numbers (ideally should be specified in the question…otherwise answer would be infinity)

No side can be 10 or more. So start with 9:

9 8 3

9 7 4

9 6 5

8 7 5

Hence 4 such triangles I think.

ok .. got it sir..thanks:)