@Sarling,
It's okay. Maybe it's the way I am explaining it.
First thing, the problem said interest is earned the average capital balance accounts. And second it says RESIDUAL P/L is divided equally. Right now NI is only $4000, but its going to change as we allocate interest on the average capital balance of both of the partners.
The Average Capital Balances are
Y:$160,000
Interst-160,000*.10=16,000
Z:$100,000
Interest-100,000*10=10000
Total Interest: 10,000+16,000=26,000
This interest Increase the capital accounts, but also decrease the net income.
New Net Income :(26,000)+4000=(22,000)
Net Income Allocation (22,000)/2=(11,000)
Y's Net Change in the account= 10,000+(11,000)= (1000)
If it makes it easy, think of it as allocating salaries. Once you allocate salaries, it decreases your net income. And the remainder of the income is allocated equally.
I would like to know your calculations, and how you are getting $1000.