The present age of Boby is equal to Abby’s age 8 years ago. Four years hence, the ratio of Abby’s age to Boby’s age will be 5 : 4. What is Boby’s present age?
24 years
32 years
40 years
20 years
28 years
Solution
Let the present age of Boby be x years and that of Abby be y years.
Then, x = y – 8 ... (i)
Now, four years hence
$\dfrac {x + 4}{x + 4} = \dfrac {5}{4}$
or, $4y + 16 = 5x + 20$
or, $4y + 16 = 5(y - 8) + 20$
or, $4y + 16 = 5y – 40 + 20$
or, $y = 36 $ years
Hence Boby’s present age = 36 – 8 = 28 years