Determine the common difference for each arihmetic sequence 1,5,9,13

The common difference is 4. If you look at the numbers 1 and 5, there is a difference of 4. If you look at 5 and 9, there is also a difference of 4. If you look at 9 and 13, there is a difference of 4. Therefore, in this arithmetic sequence, the common difference is 4.

In the sequence, the numbers are increasing by 4 each time.
So the common difference is 4.
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The method to find the female dormitory is 2-d=800

3cm and 6 and 9 cm that a possibility of that question