On a certain planet where people usually tend to live for more than a century, the ratio of present ages of father and son is 7:4. 10 years later, the ratio of their ages will be 5:3. What is the sum of their present ages?
Choose the correct choice from the following options
A) 220  B) 200  C) 140  D) 80  E) 60

Rationale: the ratio of present ages of father and son is 7 : 4 , so suppose the present ages are 7 x and 4 x , respectively . 10 years later , the ages of father and son , respectively , shall be 7 x + 10 and 4 x + 10 . the ratio of ages 10 years later is given to be 5 : 3 . this means ( 7 x + 10 ) / ( 4 x + 10 ) = 5 / 3 solving we get x = 20 . so present age of father is 7 x = 140 and present age of son is 4 x = 80 . the sum of present ages is thus 220 . ans a
Answer: A