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Present age of Tony = t
Present age of Sister = s
Tony is 5 years older means if we add 5 to present age of his sister both will be of equal age
t=s+5 ..........(1)
In three years means we have to add 3 in the present ages of both
t+3=s+3
then he will be twice as old as his sister
t+3=2(s+3)
t+3=2s+6
t=2s+6-3
t=2s+3
Put the value of t in from (1) to above equation
s+5=2s+3
s=2s+3-5
s-2s=3-5
-s=-2
Multiply by (-1) both sides of the equation
(-1)(-s)=(-2)(-1)
s=2
Put the value of s in (1), we have
t=s+5 ..........(1)
t=2+5
t=7
Present age of Tony = t = 7 years old
Present age of Sister = s = 2 years old
