Question 44145

A = proportion of coffee beans that sell for $9 per pound 
B = proportion of coffee beans that sell for $12 per pound

A and B are percentages written in decimal form (e.g. 50%=0.5), and make the whole mix:
A+B=1 ..........................i

The price of the mixture is $11.25 per pound:
A($9)+B($12)=$11.25.............ii

Rearrange equation (i) to give B in terms of A:
B=1-A...........................iii

Substitute equation (iii) into equation (ii) for B:
A($9)+(1-A)($12)=$11.25.........iv

12-3A=11.25
3A=0.75
A=0.25..........................v
Substitute equation (v) into equation (iii) for A to give:
B=0.75

So quarter of the mixture is made of "type A" beans and the remaining three quarters of the mix consists of "type B" beans.

I hope this helps 
P.S. I am trying to start up my own homework help website. I would be extremely grateful if you would e-mail me some feedback on the help you received to adam.chapman@student.manchester.ac.uk