Question 74709
Let x=amount of 50% corn that must be mixed with the 400 lb of 80% corn

Now we know that the amount of pure corn before the mixture takes place must equal the amount of pure corn after the mixture takes place.  So our equation to solve is:

0.50x+0.80(400)=0.75(400+x)  get rid of parens

0.50x+320=300+0.75x  subtract 0.75x and also 320 from both sides

0.50x-0.75x+320-320=300-320+0.75x-0.75x  collect like terms

-0.25x=-20  divide both sides by -0.25x

x=80 lb of 50% corn must be added-----------------ans

CK  

80(0.50)+0.80(400)=480(0.75)
40+320=360
360=360


Hope this helps----ptaylor