Two persons, A and B, start from the same point and travel from Chandigarh to Ambala. The distance between Chandigarh and Ambala is 60 km. Speed of A is 4km/hr slower than B. B, when he reaches Ambala, starts back via the same route without taking any rest and meets A, who was still 12km away from Ambala. Find the speed of A.

Let the speed of B be v km/h. The speed of A is 4km/hr slower than that of B. Thus, the speed of A will be (v - 4) km/h. 

B, when it reaches Ambala, starts back via the same route without taking any rest and meets A, who was still 12km away from Ambala. The distance between Chandigarh and Ambala is 60 km. 

When A and B are meeting, A is 12 km away from Ambala, which means that he has covered 48 km. At that point in time, B has covered [60 + (60 - 48)] = 72 km. 

So we can say that in time T (let's assume), A has covered 48 km and B has covered 72 km. 

$$(v-4)\timesT=48$$
$$v\timesT=72$$

$$\dfrac{v-4}{v}=\dfrac{48}{72}$$

$$3v-12=2v$$

$$v=12$$

Speed of A = (v - 4) = (12 - 4) = 8 km/h