Question 122178
r = Ricardo's age
s = sister's age
{{{r = 2s - 4}}}
{{{r + s = 20}}}
{{{s = 20 - r}}}
Substitute this value of {{{s}}} in 1st equation
{{{r = 2s - 4}}}
{{{r = 2*(20 - r) - 4}}}
{{{r = 40 - 2r - 4}}}
{{{3r = 36}}}
{{{r = 12}}} answer
check answer
{{{r + s = 20}}}
{{{12 + s = 20}}}
{{{s = 8}}}
{{{r = 2s - 4}}}
{{{12 = 2*8 - 4}}}
{{{12 = 16 - 4}}}
{{{12 = 12}}}
OK