Saba, Rayan and Derin are cooperating to complete a task. They each work at a constant rate independent of whoever else is working on the task. When all three work together, it takes 5 minutes to complete the task. When Saba is working with Derin, the task takes 7 minutes to complete. When Rayan is working with Derin, the task takes 15 minutes to complete.
How many minutes does it take for Derin to complete the task on his own?
Select one option, then click Submit.
21
28
35
48
105
Select an option, then submit.
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