Solver isn't returning feasible result: simple mfg question

[ersterli]

I'm trying to use Excel solver to solve a simple optimization problem (example attached).

The problem is set up such that the demand of a product (say, boxes) requires a certain number of machines to exist in a manufacturing site to produce those boxes. And the question is how much product (boxes) would it take to fill up the manufacturing site with machines to a certain target (say, 95%).

So overall,

- There is one objective: to force cell C10 to equal 95% or as high as the constraints allow
- There are two constraints: cell C4 cannot exceed the constraint written in cell C1; and cell C11 cannot exceed the total cost constraint written in cell C2
- There is one lever to change, in order to achieve the solve: cell C4.

When I try to set this up, the solver tells me that there is an infeasible solution, and I can't figure out why. Even if I get rid of the constraints, to error check what I've done, the solver runs but doesn't actually give me an optimized result. So I'm looking for help on what I'm doing wrong about setting up this problem with the solver.

Thanks in advance!

2021-10-28 solver example.xlsx
	A	B	C
1	Constraints	# boxes demand	1500
2		Total required cost $$	$ 2,000,000
3
4	Input parameters	Boxes to produce	1,000
5		Available mfg site space	2,000
6		Space per machine	150
7		Cost $$ per machine	1,000
8
9	Output parameters	# machines reqd	621
10		% of mfg site filled	47%
11		Total required cost $$	$ 621,000
Sheet1

Cell Formulas
Range	Formula
C9	C9	=ROUNDUP(C4*5000/10080/0.8,0)
C10	C10	=ROUNDUP(C9*C6/C5/100,2)
C11	C11	=C9*C7

Named Ranges
Name	Refers To	Cells
solver_adj	=Sheet1!$C$4	C9
solver_lhs2	=Sheet1!$C$4	C9
solver_lhs3	=Sheet1!$C$4	C9

 

[JGordon11]

Solver can't work with your ROUNDUP functions. When I removed them it worked as expected. You'll need to solve first then round up or down from the solver solution.