SOLUTION: Mike is twice as old as his sister. Together, their ages add up to 30. How old are Mike and his sister?

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Question 1015951: Mike is twice as old as his sister. Together, their ages add up to 30. How old are Mike and his sister?
Found 2 solutions by fractalier, Herdaysoji:
Answer by fractalier(6550) About Me  (Show Source):
You can put this solution on YOUR website!
Call Mike's and his sister age, m and s. Then we have
m = 2s and
m + s = 30
Substitute the first equation into the second and get
2s + s = 30
3s = 30
s = 10 and then
m = 20

Answer by Herdaysoji(25) About Me  (Show Source):
You can put this solution on YOUR website!
Let mike be x and sister be y
mike is twice his sister age
.'.x=2y
sum of thier age is 30
.'. x+y=30
since x=2y
.'.2y+y=30
3y=30
y=30/3
y=10 and x= 20