Sachin is 40 years old and Ajith is 60 years old. How many decades ago was the proportion of their ages 3 : 5?  Choose the correct choice from the following:  A) 10  B) 69  C) 37  D) 21  E) 20
A   10   If the ratio was 3 : 5, ‘A’ years ago.   Then, 710 – 610 = 4   10 = 4   Then, {( 40 – 10)/(60 – 10)}= (3/5)   5 (40 – 10) = 3(60 – 10)   210 = 20   10 = 10
<result>A</result>
Sachin is 40 years old and Ajith is 60 years old. How many decades ago was the proportion of their ages 3 : 5?