(d) the average speed of a particle (defined as total path length divided by the time taken to cover the path) is either greater or equal to the magnitude of average velocity of the particle over the same interval of time,
(e) Three vectors not lying in a plane can never add up to give a null vector.
(d) True, because the total path length is either greater than or equal to the magnitude of the displacement vector.
(e) True, as they can not be represented by the three sides of a triangle taken in the same order.