Which of the following statements are sufficient to find the age of A if:
(i) The ratio of A and B's ages was 2 : 1 five years back.
(ii) The ratio of age at present is 11 : 6.
(iii) The ratio of age 20 years back was 7 : 2.

If we take :

(i) The ratio of A and B's ages was 2 : 1 five years back.
(ii) The ratio of age at present is 11 : 6.

$$\frac{A_{present\ age}-5}{B_{present\ age}-5}=\frac{2}{1}$$

or, $$A_{present\ age}-5=2B_{present\ age}-10$$

or, $$A_{present\ age}-2B_{present\ age}=5-10=-5.$$.............(1)

And, $$\frac{A_{present\ age}}{B_{present\ age}}=\frac{11}{6}.$$..................(2)

So, By solving (1) and (2) we can get their ages.

If we take :

(ii) The ratio of age at present is 11 : 6.
(iii) The ratio of age 20 years back was 7 : 2.

$$\frac{A_{present\ age}}{B_{present\ age}}=\frac{11}{6}.$$.............................(1)

And, $$\frac{A_{present\ age}-20}{B_{present\ age}-20}=\frac{7}{2}.$$.................(2)

By solving (1) and (2) we can get their ages.

If we take : 

(i) The ratio of A and B's ages was 2 : 1 five years back.
(iii) The ratio of age 20 years back was 7 : 2.

$$\frac{A_{present\ age}-20}{B_{present\ age}-20}=\frac{7}{2}.$$..........................(1)

$$\frac{A_{present\ age}-5}{B_{present\ age}-5}=\frac{2}{1}$$...............................(2)

By solving (1) and (2) we can get their ages.

So, A is correct choice.