Question 662581
I think the original solver got this one wrong.
Let m = my age now, and h = his age now.  My age is now 4 times is, so:
{{{m = 4*h)}}}
Twenty years later, his will be half mine, so:
{{{(m+20)/2 = h + 20}}}
Substituting 4*h for m (from the first equation) gives:
{{{(4*h + 20)/2 = h + 20}}}
{{{2*h + 10 = h + 20}}}
Subtracting h + 10 from each side gives:
{{{2*h + 10 - (h + 10) = h + 20 - (h + 10)}}}
{{{2*h + 10 - h - 10 = h + 20 - h - 10}}}
{{{h = 10}}}
So his age is currently 10 and mine is 40.