Final answer:
Krystal must add 10 ounces of peanuts.
Step-by-step explanation:
To find the number of ounces of peanuts Krystal must add, we can set up an equation based on the given information. Let x represent the number of ounces of peanuts. The equation is:
20(0.40) + x(1) = (20 + x)(0.50)
Solving for x, we get x = 10 ounces.