dplyr exercises part 1a

Grouped mutate

1. Which month is busiest in terms of miles flown?

   Hint: Compute the share of yearly miles flown of each airline in each month.

2. Compute the ground time for each airplane on any given day. Make sure that you add only positive numbers.

   Hint: Use lag() or lead().

3. Find more exercises in Section 5.7.1 of r4ds.