Question 104508
Ok Jessica, here we go:
1. {{{1/p - 1/q = 1/f}}} It will simplify things a bit if we first subtract the fractions on the left side.
{{{(q-p)/pq = 1/f}}} Now multiply both sides by f.
{{{f((q-p)/pq) = 1}}} Now multiply both sides by the inverse of {{{((q-p)/pq)}}}.  This is the same as dividing both sides by {{{((q-p)/pq)}}}
{{{f = (pq/(q-p))}}}

2. {{{A = (h(a+b))/2}}} Solve for b. First, multiply both sides by 2.
{{{2A = h(a+b)}}} Now divide both sides by h.
{{{2A/h = a+b}}} Finally, subtract a from both sides.
{{{(2A/h)-a = b}}}

3. {{{V = (Q/r[1])-(Q/R[2])}}} Solve for Q (I hope I interpreted this correctly!) First, factor the Q.
{{{V = Q((1/r[1])-(1/R[2]))}}} Simplify the right side.
{{{V = Q((R[2]-r[1])/r[1]R[2])}}} Now multiply both sides by the inverse of {{{((R[2]-r[1])/r[1]R[2])}}}
{{{V(r[1]R[2]/(R[2]-r[1])) = Q}}}
Done!