Question

12 year old karun is three times as old as his brother rahul. How old will karun be when he is twice as old as rahul?

Answer 1

Let the age of his brother rahul be x years

So age of karun = 3x years [ 3 times the age of rahul ]

But in the question it is given that the age of karun is 12 years.

Then, 3x years = 12 years

= > 3x = 12

= > x = 12 / 3

= > x = 4

Substitute the value of x in age of rahul & karun.

Age of rahul = x years = 4 years

Age of karun = 3x years = 3( 4 ) years = 12 years

Let after a years, karun will be twice of his brother.

age of karun + a years = 2( age of rahul + a years )

= > 12 + a = 2( 4 + a )

= > 12 + a = 8 + 2a

= > 12 - 8 = 2a - a

= > 4 = a

Therefore, after 4 years karun will be twice as old as rahul.

Age of rahul after 4 years = 12 + 4 = 16 years

Hence, karun will be 16 years old when he is twice as old as rahul.

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Answer 2

Here is your solution

Let

The age of his brother rahul be x years

so  age of karun = 3x years

A/q

it is given that the age of karun is 12 years.

3x years = 12 years

=> 3x = 12

=> x = 12/3

=> x = 4

Putting the value of x in age of rahul & karun.

so

Age of rahul = x years = 4 years

Age of karun = 3x years = 3( 4 ) years = 12 years

Now

A/q

Let a year karun will be twice of his brother.

Age of karun + a years = 2( age of rahul + a years)

=> 12 + a = 2(4 + a)

=> 12 + a = 8 + 2a

=> 12 - 8 = 2a - a

=> 4 = a

Hence,

Age of rahul after 4 years = 12 + 4 = 16 years

Hope it helps you