Let's break down the problem from the image.

Part (a):

We know that last year there were 4 girls and 16 boys in the sports team. The central angle for the girls' section in the pie chart last year was 72° (as shown in the chart), and for the boys, it was 288°.

This year, the number of girls doubled while the number of boys remained the same. So, this year there are 8 girls and 16 boys.

Since the total number of members has increased, the central angle for the girls' section will also increase. Specifically, because the number of girls doubled, their proportion relative to the total will increase, and thus the central angle for the girls will be larger compared to last year.

Sentence for (a):

The central angle of the girls' section in this year's pie chart will increase compared to last year because the number of girls doubled while the number of boys remained the same.

Part (b):

To calculate the central angle of the girls' section in the pie chart this year:

• Last year, there were $4 + 16 = 20$ members in total.
• This year, there are $8 + 16 = 24$ members in total.

The girls make up $\frac{8}{24} = \frac{1}{3}$ of the total members.

The total angle of a pie chart is always 360°. Therefore, the central angle for the girls' section will be:

$\text{Girls' central angle} = \frac{1}{3} \times 360^\circ = 120^\circ$

So, the central angle of the girls' section this year is 120°.

Would you like further clarification on this, or any details about how pie chart angles are calculated? Let me know if you have any questions.

Here are some related questions you might want to explore:

1. What is the central angle for the boys' section this year?
2. How would the pie chart change if the number of boys doubled next year?
3. How do we calculate the proportion of each section in a pie chart based on group sizes?
4. How does the total number of members affect the angles in a pie chart?
5. Can you think of other scenarios where we could use pie charts to represent data?

Tip: When working with pie charts, always remember that the total angle must add up to 360°, so each section is a proportion of the total!