A number is 2/3 of another number. Both added together equals 50.
One of these numbers consists of three parts, and the other consists of two of those three parts. So, there are 5 equal parts in total.
Thus we need to divide 50 by 5. 50 divided by 5 equals 10.
The first number, which has three parts, is 30. The second number, which as two parts, is 20.
I hope this makes sense to you. :D Good luck in all your studies!