Answer:
State A loses a seat to State B when the total is increased
Explanation:
The "work" is most easily done by a spreadsheet, as the calculations are easily defined and very repetitive.
The "fair share" of seats is the fraction the population is of the total, multiplied by the total number of seats. It will generally be a mixed number (integer plus fraction).
If the whole number is 1 or greater, the number of seats allocated at least that whole number.
If not all seats are allocated, the fractions are sorted in decreasing order, and 1 additional seat is added to the allocation for each state, working down the list, until all of the seats are allocated.
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The attachment shows State A has the highest fraction when the number of seats is 24. Only one additional seat needs to be allocated in that case. State A gets that extra seat.
When the number of seats is 25, States B and C have the highest fractions. Each of them gets one additional seat, and State A gets no additional seats. This results in the appearance of State A giving up a seat to State B.
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Additional comment
Hamilton's apportionment method was used for a number of years in the US. The method now in use is substantially different. The current method would divide the 24 seats so that A=3, B=6, C=15. The 25th seat would be given to State A.