The next number in the series is 1/5, 1/9, 1/13, 1/17

The correct answer is 1/21. To find the next number in the series 1/5, 1/9, 1/13, 1/17, we need to observe the pattern in the denominators while the numerator remains constant at 1. The denominators are 5, 9, 13, 17.

• The difference between consecutive denominators is consistent: 9 - 5 = 4, 13 - 9 = 4, 17 - 13 = 4.
• This indicates an arithmetic progression where each term increases by 4.
• Therefore, the next denominator in the sequence will be 17 + 4 = 21.
• With the numerator remaining 1, the next number in the series is 1/21.