The speeds of two cars A and B are in the ratio 3 : 2. Car A travels for 4 hours, while Car B travels for 5 hours. If the difference between the distances covered by the two cars is 20 km, then find the speed of Car B (in km/hr).

The correct answer is 20.

Step 1: Understand the given ratios and variables.
Let the ratio of the speeds of Car A and Car B be 3 : 2.
Therefore, we can represent the speed of Car A as $s_A=3x$ km/hr and the speed of Car B as $s_B=2x$ km/hr, where $x$ is a positive constant.

Step 2: Express the distance covered by each car.
Using the formula $\text{Distance}=\text{Speed}\times \text{Time}$:

For Car A:
Time taken by Car A ($t_A$) = 4 hours.
Distance covered by Car A ($d_A$) = $3x\times 4=12x$ km.

For Car B:
Time taken by Car B ($t_B$) = 5 hours.
Distance covered by Car B ($d_B$) = $2x\times 5=10x$ km.

Step 3: Set up the equation using the given difference in distances.
We are given that the difference between the distances covered by the two cars is 20 km.

$d_A-d_B=20$

Substitute the expressions for $d_A$ and $d_B$ into the equation:

$12x-10x=20$

$2x=20$

$x=10$

Step 4: Calculate the speed of Car B.
The speed of Car B is given by $s_B=2x$.

$s_B=2\times 10=20$ km/hr.

Thus, the speed of Car B is 20 km/hr.