In nine innings of cricket, the average of a batsman is 55 runs. How many runs does he need to make in the tenth innings to get the average score 58 ?

85

Mean = \(\frac{sum\; of\; all\; the\; observations}{total \;number\; of \;observations }\)

He has mean score of 55 in 9 innings.

Hence, the total score of 9 innings =55 × 9 = 495

Let's assume he score x runs in 10th innings.

So his total score of 10 innings = 495 + x     ------(1)

Average after 10th inning = 58 ( given )

Hence, his total score in 10 innings = 10 × 58 = 580   -----(1)

Therefore, 580 = 495 + x

x = 580 − 522 = 85 runs.