Question 81329
1/f = 1/p + 1/q. Solve for p. 
Multiply everything by the LCD fpq:
{{{fpq/f=fpq/p+fpq/q}}}  Cancel matching numerators and denominators.
{{{pq=fq+fp}}} Get all p's on the same side of the equal sign.
{{{pq-fp=fq+fp-fp}}}
{{{pq-fp=fq}}} Factor out the p.
{{{p(q-f)=fq}}} Divide both sides by q-f.
{{{p(q-f)/(q-f)=fq/(q-f)}}}  
{{{highlight(p=fq/(q-f))}}}
Happy Calculating!!!!