Question 320713
Let Jerry's age be {{{J}}}, Grandpa's {{{G}}}.
Fifteen years ago, Jerry was {{{J-15}}}, Grandpa was {{{G-15}}}.
{{{J-15=(1/3)(G-15)}}}
{{{3J-45=G-15}}}
1.{{{3J=G+30}}}
Then also,
{{{G+J=110}}}
{{{J=110-G}}}
Substitute this into eq. 1,
{{{3(110-G)=G+30}}}
{{{330-3G=G+30}}}
{{{4G=300}}}
{{{highlight(G=75)}}}
.
.
.
{{{J=110-G}}}
{{{J=110-75}}}
{{{highlight(J=35)}}}