Mean weight of 21 boys is 40Kg. If mean of the first 10 boys is 42 kg and that of last 10 boys is 38 kg. Find the weight of 11th boy
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Mean weight of 21 boys = 40 kg
⇒ Weight of 21 boys = 40 * 21 = 840 kg
Mean weight of first 10 boys is 42 kg
⇒ Weight of first 10 boys = 42 * 10 = 420 kg
Mean weight of last 10 boys = 38kg
⇒ Weight of last 10 boys = 38 * 10 = 380 kg
Hence the weight of 11 boy = 840 - (420 + 380)
= 840- 800 kg
= 40 kg
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