when?till?

[norwolf]

i wonder which sentence below is correct:
they kept trying when they knew it was hopeless.
they kept trying till they knew it was hopeless.
could i get help from native speakers?
thanks a million

[buggles]

i wonder which sentence below is correct:
they kept trying when they knew it was hopeless.
they kept trying till they knew it was hopeless.
could i get help from native speakers?
thanks a million

If they kept trying when it was useless, they kept on trying even though it was useless.
If they kept trying till it was useless, then they gave up trying once they had realised it was useless.
Buggles (Native speaker, but not a teacher).

[katka.pospi]

The correct sentence is - They kept trying TILL they knew it was hopeless.

[Anglika]

The correct sentence is - They kept trying TILL they knew it was hopeless.

As indicated above by Buggles - that will depend on the context of the sentence.