A recipe calls for mixed nuts with 50% peanuts. 1/2 pound of 15% peanuts has already been used. How many pounds of 75% peanuts needs to be added to obtain the 50% mix?

Now you have

(.15) 0.5 lb peanuts = 0.075 lb peanuts

0.5 lb nuts 0.5 lb nuts

for every pound of 75% mixed nuts you add, you get. 75 lb peanuts, how many pounds, x, do you need to add to get the ratio 50 to 100?

0.075 lb peanuts + 0.75x lb peanuts = 50

0.5 lb nuts + x lb nuts 100

cross multiply

(0.075 +.75x) 100 = (0.5 + x) 50

7.5 + 75x = 25 + 50x

25x = 17.5

x = 0.7 lb of 75% peanuts