math
posted by harry on .
can you solve this equation by using simultaneous equations and can you write the method please?
Sarah and Louise have a combined age of 24. Six years ago Sarah was triple Louise's age. What is Sarah and Louise's ages now. Let Sarah be x and Louise be y.
thankyou
Harry

S + L = 24
(S6) = 3 (L6)
solve first for L
L = (24  S)
Multiply second out
S  6  3 L  18
S = 3 L 12
substitute our L from the first equation in the second equation
S = 3 (24  S)  12
S = 72  3 S 12
4 S = 60
S = 15
then use the first equation to find L
L = 24  15
L = 9
then check
Now
15 + 9 = 24 , yes they add to 24 check
Six years ago
156 = 9
9  6 = 3
sure enough, 9 is three times 3, check 
S + L = 24
(S6) = 3 (L6)
solve first for L
L = (24  S)
Multiply second out
S  6 = 3 L  18
S = 3 L 12
substitute our L from the first equation in the second equation
S = 3 (24  S)  12
S = 72  3 S 12
4 S = 60
S = 15
then use the first equation to find L
L = 24  15
L = 9
then check
Now
15 + 9 = 24 , yes they add to 24 check
Six years ago
156 = 9
9  6 = 3
sure enough, 9 is three times 3, check