Average weight rises when one person of 51 kg is replaced: weight of the newcomer

The same question, asked 2 times: 20 Jul 2023 S2*, 18 Sep 2024 S2. Every wording below, oldest first.

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Question 1
20 Jul 2023 S2
65 $The average weight of 15 persons is increased by 1.2 kg when one of them whose weight is 51 kg is replaced by a new man. The weight of the new man is:$
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Question 2
18 Sep 2024 S2
69 $The average weight of 10 students is increased by half a kg when one of the students weighing 51 kg is replaced by a new student. Find the weight of the new student.$
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