In covering a distance of 72 km, Amit takes 5 hours more than Vinay. If Amit doubles his speed, then he would take 7 hour less than Vinay. Amit's speed is:

Correct option is B

​Given:​

Distance covered = 72 km

Amit takes 5 hours more than Vinay to cover the distance.

If Amit doubles his speed, he would take 7 hours less than Vinay.

Formula Used:

Time = $$\frac{\text{Distance}}{\text{Speed}}$$​​

Solution:

Let the speed of Amit be a km/h and the speed of Vinay be v km/h.

From the first conditions;

​​​​$$\frac{72}{a} - \frac{72}{v} = 5$$...(1)​

​​​From the second condition;

​$$\frac{72}{v}-\frac{72}{2a}=7$$....(2)

adding (1) and (2) 

$$\frac{72}{a}-\frac{72}{2a} = 12 \\ \ \\ \frac{72-36}{a} = 12 \\ \ \\ \frac{36}{a} = 12 \\ \ \\ \implies a = 3 \ km/h$$​​

Thus, Amit's speed is 3 km/h.