Given: Average weight of 12 people and the trainer = 66 kg Calculation: The weight of 12 students and the trainer =13×66 ⇒ 858 kg Total weight excluding the trainer =68×12 ⇒ 816 The weight of the trainer ⇒858–816 ⇒ 42 kg ∴ The weight of the trainer is 42 kg.