For the following question:
Pedro travels by bus to school at an average speed of $40$ km/hr. He is driven home by the same route by a friend's car at an average speed of $50$ km/hr. Which of the following is greatest:
(a) Average speed of both legs of the journey.
(b) $45$.
According to the book, the answer is (b). How did they calculate average speed here? I know that the formula for average speed is $A_v=\frac{Total~ Distance~ Covered}{Total~ Time ~Taken }$. Here we only know the velocity.