Question 1091694
 Ama's age is two thirds that of her sister.
 four years ago Ama's age was half the sister.
 how old is the sister
:
let a = A's age
let s = sis's age
:
Write an equation for each statement

  Ama's age is two thirds that of her sister.
a = {{{2/3}}}s
:
 four years ago Ama's age was half the sister. 
a - 4 = {{{1/2}}}(s-4)
Multiply both sides by 2
2(a-4) = s - 4
2a - 8 = s - 4
2a = s - 4 + 8
2a = s + 4
replace a with {{{2/3}}}s
2({{{2/3}}}s) = s + 4
{{{4/3}}}s = s + 4
multiply both sides by 3, get rid of the annoying fraction
4s = 3(s+4)
4s = 3s + 12
4s - 3s = 12
 s = 12 yrs is the sister's age
:
;
you should find a and then check the solutions in the 2nd statement