Question : The average weight of 10 boys is increased by 3kg if one of them weighing 40 kg is replaced by a new boy. The weight of the new boy is:
Option 1: 45 kg
Option 2: 70 kg
Option 3: 80 kg
Option 4: 40 kg
Correct Answer: 70 kg
Solution :
Let the average weight of 10 boys be $x$.
The sum of weights of 10 boys = $10x$
New average weight = $x+3$
New sum of weights = $10(x+3) = 10x+30$
Let the weight of the new boy be $y$.
So, $10x-40+y=10x+30$
⇒ $y=30+40=70$
Hence, the correct answer is 70 kg.
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