Answer:
Mary is 4 year is now. The sister is 2 years old now.
Explanation:
Let m = Mary's age now.
Let s = the sister's age now.
"Mary is twice older than her sister"
m = 2s
In 5 years, Mary's age will be m + 5, and the sister's age will be s + 5.
"in 5 years time she will be 2 years older than her sister"
m + 5 = (s + 5) + 2
m + 5 = s + 7
m - s = 2
We have a system of equations.
m = 2s
m - s = 2
Substitute 2s for m in the second equation.
2s - s = 2
s = 2
The sister is 2 years old now.
m = 2s = 2 × 2 = 4
Mary is 4 year is now.