Final answer:
The central angle of Cindy's slice is 120 degrees.
Step-by-step explanation:
To find the central angle of Cindy's slice, we need to determine the proportion of her age to the total age of all three people. The total age is 10 + 15 + 20 = 45 years. Cindy's proportion is 15/45 = 1/3. To find the central angle, we multiply this proportion by 360 degrees, which is the total angle for a full circle. So, Cindy's slice has a central angle of (1/3) * 360 = 120 degrees.