by Sahana
(Kolkata)
Arvind is eight years older than his sister. In three years, he will be twice as old as his sister. how old are they are now?
Solution
Let x be a Arvind's age.
Let x  8 be his sister's age.
In 3 years, Arvind's age will be x + 3
In 3 years, the sister's age will be x  8 + 3 = x  5
In 3 years, Arvind is twice as old as his sister.
x + 3 = 2 × (x  5)
x + 3 = 2x  10
2x  10 = x + 3
Subtract x from both sides.
2x  x  10 = x  x + 3
2x  x  10 = 3
Add 10 to both sides
2x  x  10 + 10 = 3 + 10
2x  x = 3 + 10
x = 13
Arvind's age is 13
His sister's age is 13  8 = 5.
In 3 years, Arvind's will be 16 and the sister will be 8.
16 is twice as big as 8.
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