SOLUTION: 4 pounds of wheat at $1.5 is mixed with 8 pounds of wheat at $2 per pound. find the average price of the mixture?

The worth will be the same after mixing that it was before mixing.

The 4 pounds of $1.5 wheat is worth 4·$1.5 = $6
The 8 pounds of $2 wheat is worth 8·$2 = $16

So together the 4+8 or 12 pounds is worth $16+$6 = $22

That's what the 12 pounds of wheat will be worth after
the two get mixed.

To find out how much that would be per pound, we divide 

$22 by 12 pounds and get $1.83 1/3.

[As a rough check, since we mixe more of the $2 wheat than the 
$1.5 wheat, we should expect that the answer be closer to $2
than to $1.5]

Edwin