Let x=amount of nuts needed that sell for 3.10/lb.
Let y=amount of nuts needed that sell for 5.70/lb.
You need to solve the following 2 equations simultaneously:
x+y= 5.2 lbs.
Change the first equation to get an expression you can use to substitute in for x or y in the second equation:
either x=5.2-y or y=5.2-x, pick one of these & plug it into the second equation: now you have an equation with a single variable (x or y) depending on which one you picked. Now solve for that variable:
3.1(5.2-y)+5.7y=4.00 *remember to use the order of operations when you solve it*
12.12=2.6y *I want to work with positive numbers*
4.66153846=y * round to 2 decimal places*
y=4.66, which is the amount of nuts(in lbs) you need of the nuts that sell for 5.70/lb.
we know x+y=5.2, so if y=4.66, then just substitute 4.66 in the equation and solve for x:
x=5.2-4.66=.054, which is the amount of nuts you need (in lbs) that sell for 3.10/lb.