I’ve seen Duolingo mentioned in posts and so I checked it out and started the test that it offered. It asked to translate ‘Tri tynnu dau yn hafal i yn’ which I translated as ‘Three minus two equals one’. Wrongly it seems. I interpreted this as I would say/write the sentence in English. I then read some responses re. the use of tynnu/take away. One person (don’t know nationality) thought that the use of tynnu seemed to be juvenile in this context. Another (from Duolingo?) was that the use of the verb ‘to subtract’ (which I take also to include ‘minus’) is old fashioned (I certainly wouldn’t use ‘take away’ unless to a child). Another suggestion seemed to be that was that because ‘take away/tynnu’ is used by native youth speakers that it’s the ‘correct way’. As a non native learner, I’m wondering about and interested if SSIW members have any opinions on the matter.
I’ve certainly seen it suggested that the use of “take away” was because many parents learn Welsh when their kids start school and it’s the phrase used with small children, so that’s what’s taught to parents so they can use the same terms.
Yes @margarethall, that’s the impression that I got. I can’t imagine that Welsh adults would use tynnu in that context unless they were talking to children. But then I thought that this was just me not having as yet sufficient ‘feel’ for the spoken language and simply putting an English slant on it.
I think this is just Duolingo have a certain lack of flexibility when there is more than one way to say things (not that I know much about it) - but your translation there is absolutely right - although ‘tynnu’ is probably used for ‘minus’ more often in Welsh than ‘take away’ is in English… 
Seems that way @aran. Since I’d seen the site mentioned I thought that I’d have a look at it. Think that I’ll forget about it. 
Me too!