Question 357298
Let x = #lbs that has to be taken and replaced.  Then
{{{0.40*20 -0.40x + 0.00x = 0.20*20}}},
{{{8 -0.40x = 4}}},
{{{4 = 0.40x}}},
{{{x = 10}}}.  10 lbs of the mix must be replaced with pure cashews.