We have been given the cost of peanuts as $1.90/lb and cost of raisins as $2.50/lb.
We need to figure out how much of peanuts should be mixed with raisins to make 12 pounds of trail mix that costs $2.05/lb.
Let x pounds of peanuts should be mixed with (12-x) pounds of raisins. Therefore, we can set the total cost before mixing with total cost after mixing.
![1.90x+2.50(12-x)=12(2.05)](https://img.qammunity.org/2019/formulas/mathematics/high-school/y3mfqv7ceuqsi9t1rb35lc9b0ow3tjk6a2.png)
![1.90x+30-2.5x=24.6](https://img.qammunity.org/2019/formulas/mathematics/high-school/4pyk9t80ztcmat7ds92wwf22ing8w5fprl.png)
![1.90x-2.5x=24.6-30](https://img.qammunity.org/2019/formulas/mathematics/high-school/p8droghtfl9l3y422136rxbswuutdpbxmp.png)
![-0.6x=-5.4](https://img.qammunity.org/2019/formulas/mathematics/high-school/rbvav3az74dgdi3rg56oboa697fpefft07.png)
![x=(-5.4)/(-0.6)=9](https://img.qammunity.org/2019/formulas/mathematics/high-school/n2448tp2e0ujnydms3urh1vbdabk2u3nsi.png)
Therefore 9 lbs of peanuts should be mixed with 3 lbs of raisins.