The mean weight of 21 students of a class is 52 kg. If the mean weight

1.	The mean weight of 21 students of a class is 52 kg. If the mean weight of the first 11 students of the class is 50 kg and that of the last 11 students is 54 kg, find the weight of the 11th student.
Answer» Let the weight of 11^th student be x Given that mean weight of 21 students = 52kg ∴ Sum of 21 students weight = 21 × 52 = 1092kg Mean weight of the first 11 students = 50kg Sum of first 11 students weight = 11 × 50 = 550kg Mean weight of the last 11 students = 54kg Sum of the last 11 students weight = 11 × 54 = 594kg Therefore, Sum of first 11 students weight + sum of last 11 students weight – weight of the 11^th student = sum of 21 students weight 550+594 - x = 1092 ⇒ 1144 – x = 1092 ⇒ x = 52 Hence, weight of 11^th student is 52kg

The mean weight of 21 students of a class is 52 kg. If the mean weight of the first 11 students of the class is 50 kg and that of the last 11 students is 54 kg, find the weight of the 11th student.

Answer»

Let the weight of 11^th student be x

Given that mean weight of 21 students = 52kg

∴ Sum of 21 students weight = 21 × 52 = 1092kg

Mean weight of the first 11 students = 50kg

Sum of first 11 students weight = 11 × 50 = 550kg

Mean weight of the last 11 students = 54kg

Sum of the last 11 students weight = 11 × 54 = 594kg

Therefore,

Sum of first 11 students weight + sum of last 11 students weight – weight of the 11^th student = sum of 21 students weight

550+594 - x = 1092

⇒ 1144 – x = 1092

⇒ x = 52

Hence, weight of 11^th student is 52kg

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