Tim and Judy mix two kinds of feed for pedigreed dogs. they wish to make 28 pounds of feed worth $0.19 per pound by mixing one kind worth $0.13 per pound with another worth $0.29 per pound. How many pounds of the cheaper kind should they use in the mix?

ok, so from the problem we know after mixing we want the average pound to be worth .19, and that the total number of pounds should be 28

so we have two unknowns, and hence we need two equations to solve this

so the first one is that (.13*x + .29*y)/28 = .19

that is the direct translation of "the average pound costs .19 after adding both components together")

now the second equation we know, is that when we add the two amounts together, there are a total of 28 pounds

i.e. x+y = 28

so now you have to use substitution to get either x or y

so let's take the second equation's value of "y", which is the more expensive amount, and substitute it back into the first equation

y = 28 - x

so if we put that back into the first equation, in place of y ("substituing"), we get: .13x + .29(28 -x) = .19

can you solve for x from there?

whoops sorry, above line should ready (.13x + .29(28-x))/28 = .19

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