A runs twice as fast as B and B runs thrice as fast as C. The distance covered by C in 72 minutes, will be covered by A in :

Let C's speed = x km/hr
Then, B's speed = 3x km/hr
And A's speed = 6x km/hr
∴ Ratio of speeds of A, B, C
= 6x : 3x : x
= 6 : 3 : 1
Ratio of times taken
= $$\frac{1}{6}$$ : $$\frac{1}{3}$$ : 1
= 1 : 2 : 6
If C takes 6 minutes, then A takes 1 minute
If C takes 72 minutes, then A takes $$\left( {\frac{1}{6} \times 72} \right)$$  min = 12 min