You are in a car going 70 km/h and another car passes you going in the opposite direction at 70 km/h. do both cars have the same velocity? explain.

No, both the cars do not have the same velocity.

Velocity is a vector quantity and it is the rate of change of displacement with time or change in speed with direction.

Velocity has both magnitude and direction. So when you are in a car going 70 km/h and another car goes in the opposite direction at 70 km/h their velocities are different. 

How?

Consider your car as moving in the positive direction, so its velocity will be 70 km/h and for the car moving in the opposite direction, since the direction is opposite, the velocity of that car will be -70 km/h. This is because, the velocity is a vector quantity that has both magnitude and direction. For one car, the direction is positive and for the other one the direction is negative.