My 7 year old DD has suddenly problem with maths, please help

[Praguemummy]

She suddenly started to get very bad at maths. 2 months ago 33 + 50 was no problem for her, even when you just ask her, without writing it on the paper. And now, out of blue she has problem, or mental block as I can see that she is thinking hard but usually comes with the wrong answer. So I try to explain on the simplier example like 13 + 13, she understand we altogether come to result 26 and when I ask her next what 14 +14 she doesnt know again. Doesn't help I have no nerves and start to shout at her, poor little thing I am at the end, as if she wont move on, her school results will go horribly wrong. Please help

I expect that she has now had several ways of doing it and it confused. Don't shout!
Start with single digit numbers and make it a fun game-e.g. have cards-pick up 2 and add together. Go on to multiples of 10 and do the same with 40+60 etc.
Then use partitioning so that 14+14 = 10+10+4+4 and 33+50=30+50+3
Just relax and play games with it.

Lots of games on Woodlands Junior School site
Keep it fun-good luck.

www.mathszone.co.uk/
A lovely website

Mine had a similar thing when they started learning several different methods of doing the same thing at school. They just got confused by it. In the end, we found the method they preferred and stuck with it.