My calculations say is should be {0, 300, 99},
but Solver says {0, 300, 100}

Here's another interpretation of the problem.
Here's my best guess as to what happened.

If you read the problem as this:
For a particular item, if the number sold 99, then the price of "ALL" items
is reduced by 5%, then the solution is {0,300,99}.

However, if the first 99 items are sold at price, and only the 100th item is
reduced by 5%, then the solution is {0,300,100}.

Most problems that I've seen use this Marginal reduction in price. I
believe the Solver model that you read probably was using this
interpretation of the price reduction.

Your solution was more abrupt.
Most likely, your solution was:

300*45 + 99*40 = 17460

And if you increased the speakers by 1 (to 100), then the price off "ALL"
speakers were reduce 5% to 38.

300*45 + 100*38 = 17300

Which is less of a profit, and why you show 99.

--
HTH :)
Dana DeLouis

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