Question 1008353
Your total is 12 grams of cereal.  Let x be the amount at 40%, (12-x) be the amount at 10%. Then:
.4(x)+.1(12-x)=12(.2)
.4x+1.2-.1x=2.4
.3x=1.2
x=4
12-x=8
You need 4 gms of 40% protein cereal with 8 gms of 10% protein cereal to make 12 gms of 20% protein cereal!!!!!!!!