Question 72517
Let r=ricardo's age, s=sister's age
{{{2s-4=r}}} Here's their age relationship
{{{s+r=20}}}Sum of their ages
{{{s=20-r}}}Solve for s
{{{2(20-r)-4=r}}}Plug in s=20-r
{{{40-2r-4=r}}}solve for r
{{{36=3r}}}
{{{36/3=r}}}
{{{r=12}}}
So ricardo is 12 and his sister is:
{{{s=20-12}}}
{{{s=8}}}
Check:
{{{2(8)-4=12}}}
{{{16-4=12}}}
{{{12=12}}}Works