1
A[100]

B[priority1] (30)

C[priority2] (25)

D[priority3] (40)

(100) is a balance. I want the balance to be distributed amongst the
priority's 1-3.
(A[100]) is a growing number that starts at [0].
"B[priority1] (30)" starts to add its percentage of (A[n]) as soon as
"A" reaches [1]; then "B" stops when its total "30" is met.
"C[priority2] (25)" does not start its percentage calculations until
"B[priority1] (30)" has been satified at (30). Then any addition to
(A[n]) ie "A[31]" is added to "C[priority2] (25)" and so on.

Maybe this would be useful.

The number 100 in A1 is typed in, I presume, and may be replaced by a
different number for different cases.

In B2, B3, etc., put the threshold values 30, 25, 40, etc.

In A2, put
=MIN($A$1,B2)

In A3, put
=MIN($A$1-SUM(A$2:A2),B3)

Select A3 and extend downward as far as needed (that is, point to the
little square dot at the lower-right of A3, hold down the left mouse
button, and drag the mouse downward).