Since there are 6 number of observation in all, which is an even number of observation.

Median will be found at the aggregate of (6/2 = ) 3^rd and (6/2 + 1 = ) 4^th position.

3^rd value = x – 1 and 4^th value = x – 3

Taking their aggregate, we get

Median = (x – 1 + x – 3)/2

⇒ 13 = (2x – 4)/2 [∵ median = 13]

⇒ 26 = 2x – 4

⇒ 2x = 26 + 4

⇒ 2x = 30

⇒ x = 15

Thus, median is 15.