Two pipes together for t minutes, then rates change: more time to fill

The same question, asked 2 times: 17 Sep 2025 S1*, 19 Sep 2025 S1. Every wording below, oldest first.

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Question 1
17 Sep 2025 S1
55 $Pipe A is capable of filling a tank in 16 minutes while Pipe B can fill the same tank in 24 minutes. Both pipes are opened together, but after 4 minutes, the rate of Pipe A doubles and the rate of Pipe B becomes half of its original. How many more minutes will it take to fill the tank completely?$
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Question 2
19 Sep 2025 S1
55 $Two pipes A and B can fill a tank in 18 and 24 minutes respectively. After both are opened together for 6 minutes, the rate of pipe A becomes half, and pipe B becomes double its original. In how many more minutes will the tank be full?$
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Question 1