Question 505061: bani is 5 years older than his sister. In 3 years he will be twice as old as she is. How old is bani? Answer by Maths68(1474) (Show Source):
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Present age of Bani = b
Present age of sister = s
Bani is 5 years older than his sister means if we add 5 to sister's age both ages will be same
b=s+5...........(1)
In 3 years means we have to add 3 in their present ages
b+3=s+3
then
he will be twice as old as she is
b+3=2(s+3)
b+3=2s+6
b=2s+6-3
b=2s+3
Put the value of b from (1) to above eqution
s+5=2s+3
s=2s+3-5
s-2s=-2
-s=-2
Multiply by (-1) both sides of the equation
(1)(-s)=(-1)(-2)
s=2
Put the value of s in (1)
b=s+5...........(1)
b=2+5
b=7
Present age of Bani = b = 7
Present age of sister = s = 2
