SSC CHSL 6 Dec 2015 Shift 2 Paper

Average of 13 results = 70
⇒ Sum of 13 results = 13 × 70 = 910
Similarly, sum of first seven = 7 × 65 = 455
And sum of last seven = 7 × 75 = 525
∴ Seventh result = (455 + 525) − 910 = 70