Average weight of a group of 30 boys is 34 Kg. Later it was found that the weighing machine was showing 2 Kg more than the actual weight. What is the actual average weight?
Let the total weight of the group as measured with the faulty machine be x. Then, by average formula $34 = x/30$, which gives x = $34 × 30 = 1020$. When weight of each of the 30 boys is reduced by 2 Kg, the new total becomes $1020 - 30 × 2 = 960$, the new average becomes $960/30 = 32$. TIP: As a shortcut, the new average = old average - error in weighing machine.