For the values $x=5$, 10, 15, 20, 25 with frequencies 4, 9, f, 5, 3, the median is 15. What is the least whole-number value f can take?

13 values lie below 15 and 8 above. With N = 20 + f, the middle position(s) must fall inside the block of 15s (positions 14 to 13 + f). f = 4: N = 24, 12th/13th are 10 → no. f = 5: N = 26, 13th = 10, 14th = 15 → median 12.5 → no. f = 6: N = 27, 14th = 15 ✓. Least f = 6.