Question 315472
lynne is currently 100% older than her younger sister sylvie.
this means Lynne is Twice as old as Sylvie
L = 2S
:
in 8 years , she will be only 20% older.
L + 8 = 1.2(S + 8)
L + 8 = 1.2s + 9.6
L = 1.2s + 9.6 - 8
L = 1.2s + 1.6
:
how old is sylvie now ?
Replace L with 2S in the above equation
2S = 1.2s + 1.6
2s - 1.2s = 1.6 
.8s = 1.6
s = {{{1.6/.8}}}
s = 2 yrs Sylvie now
:
:
Check solution in the statement (Lynne is 4):
"in 8 years , she will be only 20% older. 
4 + 8 = 1.2(2 + 8)
12 = 1.2(10); confirms our solution of S = 2