To complete the "less than type frequency" column, we add the current class's frequency to the cumulative frequency of the previous class.

Here is the completed cumulative frequency table.

To complete the "less than type frequency" column, we add the current class's frequency to the cumulative frequency of the previous class.

• For Class 0-10: The frequency is 2. The cumulative frequency is 2.

• For Class 10-20: The frequency is 12. The cumulative frequency is $2 + 12 = 14$. So, the first blank is $\boxed{14}$.

• For Class 20-30: The frequency is 20. The previous cumulative frequency was 14. The cumulative frequency is $14 + 20 = 34$. So, the second blank is $\boxed{14}$.

• For Class 30-40: The frequency is 16. The previous cumulative frequency was 34. The cumulative frequency is $34 + 16 = 50$. So, the third blank is $\boxed{16}$ and the fourth blank is $\boxed{50}$.

Here is the completed table:

Class Age (in years)	frequency	less than type frequency
0-10	2	2
10-20	12	$2 + 12 = \boxed{14}$
20-30	20	$\boxed{14} + 20 = 34$
30-40	16	$34 + \boxed{16} = \boxed{50}$