The average score of a cricketer for ten matches is 38.9 runs. If the average for the first six matches is 42, then find the average for the last four matches.

Solution: 
Total sum of last 4 matches = (10 x 38.9) – (6 x 42)
                                          = 389 - 252
                                          = 137
    Average = 137/4
                 = 34.25