You wrote the calculation wrong.
When you write -30% you mean *0.7
Write 450*0.7 and you will get the correct result 315.

450 - 30%, in english, it means 30% discount of 450.
So it's difference between east and west world.

As far I know, in the occidental world (or I was living in Mars and I didn't knew) percentage calculations are made like https://bbs.deepin.org/user/73896 said, multiplying the original value with 0.* depending on the percentage you want to know, besides that, calculators (software or real ones) always have different word structures.

https://bbs.deepin.org/user/38283 Germany is in the east?!Really?!
No,I just listened to my maths teacher and didn't forget everything xD
I understand very good what you mean but software is stupid.
It can only work if you type it in the wanted way or it won't know what you want.

Edited by josemarcos at 2017-12-4 22:37

Hello everyone.

All the calculators I had, be it physical, smartphone or in Windows itself, I always used the calculation 450 - 30%. I did not know there was a differences in calculations between calculators.

The gnome calculator also calculates 450 - 30% = 315