Question 716020
Assign Variables:
M=amount of mixture before addition, 5 pounds
c=percent of mixture as peanuts before addition, 15%
p=how many pounds of peanuts to add, unknown
r=resulting percent peanuts after adding p pounds, 25%


Create Equation:
{{{highlight((M*c+p*100)/(p+M)=r)}}}, the factor of 100 with p is because p is at 100%.
Solve for p.
.
skipping the steps here
.
{{{highlight(p=M(r-c)/(100-r))}}}


Now you simply substitute the given values to calculate p.