If median and mean of the first 10 prime numbers are M and m, respectively, then:

Start by listing the first ten primes: 2, 3, 5, 7, 11, 13, 17, 19, 23, 29. Their sum is 129, so the mean m = 129/10 = 12.9.

For the median, with ten observations it is the average of the 5th and 6th values in the ordered list, which are 11 and 13. So M = (11 + 13)/2 = 12.

Hence M = 12 is less than m = 12.9, and the answer is C.

• Option A is wrong because the larger primes 23 and 29 pull the mean up, while the median sits at the middle of the ordered list.
• Option B reverses the inequality. Here the mean is the larger value, not the median.
• Option D fails because C is clearly correct.

Core concept: mean versus median in a right-skewed set. A few large values pull the mean above the median. This idea recurs in Mains data interpretation, for example when reading income or land-holding statistics.

Trap: candidates often take the median of an even-sized set as the 5th value alone, instead of the average of the 5th and 6th values.