There's really nothing to solve. If the %s have to remain the same, you
have only one variable and simple algebra will yield the answer.

In your example, B=2*A and C=5*A. So, the only variable you have to play
with is A. If the unit prices were Pa, Pb, and Pc, you would get the total
price as Pa*A + 2*Pb*A + 5*Pc*A or A(Pa +2Pb + 5Pc). Given a target of Pt,
solve for A to get A = Pt/(Pa +2Pb + 5Pc).

The generalization to 10 items is similarly straightforward.

--
Regards,

Tushar Mehta
www.tushar-mehta.com
Excel, PowerPoint, and VBA add-ins, tutorials
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In article .com,
says...
Hi Bernard,

(1) the percentage of total volume must stay same for each item !!!

E.G.:
Item A= 25 units
Item B= 50 units
Item C= 125 Units
Total = 200Units

The relative share should remain unchanged:
Being 25/200= 12.5% for A, 25% for B, 62.5% for C

Brgds Sige