Question

How many pounds of nails costing $7 per pound must be mixed with 6 pounds of nails costing $3 per pound to yield a mixture costing $4 per pound?

Answer 1

Let nails 7/pound=N1
nails 3/pound=N2

let N1=x
N2=6
then total=x+6
7x+6*3=(x+6)*4
7x+18=4x+24
3x=6
x=2
so 2 pounds on Nails costing 7/pound must be added