The average weight of 9 boxes is 61kg. If three boxes having an average weight of 70 kg are removed, then what will be the new average weight of the remaining boxes?

56.5 kg

The average weight of 9 boxes = $\frac{Sum\;of\;weights}{9}$

⇒ $\frac{Sum\;of\;weights}{9}$ = 61

⇒ Sum of all weights = 61 x 9 = 549

If three boxes of average weight 70 kg are removed, total of (70 x 3) 210 kg is removed.

Weight of 6 boxes = weight of 9 boxes - 210

                           = 549 - 210 = 339

⇒ New average = $\frac{Sum\;of\;6\;boxes}{6}$

                       = $\frac{339}{6}$ = 56.5 kg