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### Question

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?

**A**

32.

**B**

33.

**C**

31.

**D**

30.

**Soln.**

**Ans: a**

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.