In nine innings of cricket, the average of a batsman is 47 runs. How many runs does he need to make in the tenth innings to get the average score 51 ?

87

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

He has mean score of 47 in 9 innings.

Hence, the total score of 9 innings =47 × 9 = 423

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

So his total score of 10 innings = 423 + x     ------(1)

Average after 10th inning = 51 ( given )

Hence, his total score in 10 innings = 10 × 51 = 510   -----(1)

Therefore, 510 = 423 + x

x = 510 − 423 = 87 runs