To construct a frequency table for the ages of the 20 science teachers, we first group the ages into the specified intervals: 20-30, 30-40, 40-50, and 50-60.

Here are the steps to create the table:

1. 20-30: Ages falling in this interval are 25, 27, 27, 28, 29, 29, 29.
   Frequency = 7

2. 30-40: Ages falling in this interval are 30, 31, 34, 38, 38, 39.
   Frequency = 6

3. 40-50: Ages falling in this interval are 40, 42, 42, 47.
   Frequency = 4

4. 50-60: Ages falling in this interval are 50, 52, 55.
   Frequency = 3

Frequency Table:

Age Interval	Frequency
20-30	7
30-40	6
40-50	4
50-60	3

Would you like any additional details or clarifications?

Related Questions:

1. How do we calculate the relative frequency for each interval?
2. What is the modal age group in this dataset?
3. Can we compute the median and mean of this dataset?
4. How can we represent this data using a histogram?
5. What would happen if we used different intervals for grouping the data?

Tip: When choosing intervals for a frequency table, make sure the intervals are non-overlapping and cover all the data points.