Act 1
1. Which circle will fill up first?
2. Write down a guess.
Act 2
3. What information would be useful to figure this out?
4. Write down some questions you have in your head right now.
Note: The animation software animates the circles using a rate of pixels/time instead of square pixels / time.
Act 3
Sequel
5. What would happen if the blue circle was 5% larger?
6. What would happen if the yellow circle was 5% smaller?
Common Core Standards
7.RP
Analyze proportional relationships and use them to solve real-world and mathematical problems.
7.G.B.4
Know the formulas for the area and circumference of a circle and use them to solve problems; give an informal derivation of the relationship between the circumference and area of a circle.
7.RP
Analyze proportional relationships and use them to solve real-world and mathematical problems.
7.G.B.4
Know the formulas for the area and circumference of a circle and use them to solve problems; give an informal derivation of the relationship between the circumference and area of a circle.
TEKS
7.4(D)
solve problems involving ratios, rates, and percents, including multi-step problems involving percent increase and percent decrease, and financial literacy problems
7.5(C)
solve mathematical and real-world problems involving similar shape and scale drawings
7.4(D)
solve problems involving ratios, rates, and percents, including multi-step problems involving percent increase and percent decrease, and financial literacy problems
7.5(C)
solve mathematical and real-world problems involving similar shape and scale drawings
When Math Happens 
I love this resource and I share it every semester with my students! Thank you for these great resources!!
I used this task in my middle grades methods class this week and I was left with a question. If the circles are filling up with color, wouldn’t we need to determine the rate as a ratio of “square pixels/time” since we are covering an area? It appears the answers provided in act 3 are based on “pixel/time.”
Hey Shelli thank you for the kind words and the comment! Good catch! I haven’t thought about this before. You’re right that it would seem that we should be calculating square pixels/time. I’m guessing the way the software I use animates the circles is only using pixel/time. I’ll add a note to the post. Thanks for bringing this up!