Grouped ages of books

Book ages (years) are grouped into \(0\le a<10\), \(10\le a<20\), \(20\le a<30\), \(30\le a<40\), \(40\le a<50\), \(50\le a<60\) with frequencies 8, 14, 22, 18, 10, 8. Let a be the age of a book in years. A book is selected at random for the probability calculation. Find

1. the modal class,[1]
2. the estimated mean,[2]
3. \(P(\text{age}<40)\).[1]