An hour has 60 minutes.
-> 5/6 of 60 minutes
5/6*60
=50
So, 50 minutes
-> 1/2 of 60 minutes
1/2*60
=30
So, 30 minutes
-> 2/3 of 60 minutes
2/3*60
=40
So, 40 minutes.
Hope this helps. If you have any questions, please put them in the comments below.
quadratic equations can be soled by 3 methods
factorization
completing square
quadratic formula
but factorization is the simplest