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Last weekend, Colin collected red leaves for an art project. On Saturday he collected \(10\) red leaves, and on Sunday he collected some more in the park. Now he has \(20\) red leaves. Which of the following equation when solved will give how many red leaves Colin collected on Sunday?
Answer variants:
10+r=20
20÷r=10
r÷20=10
20×r=10
Note: 'r' is a variable to represent the unknown number of red leaves.