Question 175973
I'll reference their ages to 1999, and I'll say that at that year
{{{j}}}= Joy's age
{{{a}}}= Ali's age
Given:
In 1987, Joy's age was
{{{j - (1999 - 1987)}}}
{{{j - 12}}}
In 1987, Ali's age was
{{{a - 12}}}
(1) {{{j - 12 = 3(a - 12)}}}
The difference in their ages is 8 years and Ali is the younger, so
(2) {{{a = j - 8}}}
Substitute (2) in (1)
{{{j - 12 = 3*(j - 8 - 12)}}}
{{{j - 12 = 3*(j - 20)}}}
{{{j - 12 = 3j - 60}}}
{{{2j = 48}}}
{{{j = 24}}}
And, since
{{{a = j - 8}}}
{{{a = 24 - 8}}}
{{{a = 16}}}
Joy is 24 and Ali is 16 in 1999
check:
(1) {{{j - 12 = 3(a - 12)}}}
(1) {{{24 - 12 = 3(16 - 12)}}}
{{{12 = 3*4}}}
{{{12 = 12}}}
OK