The average weight of 30 students in a class is 60kg. If the weight of the class teacher is included, the average increases by 0.5kg. The weight (in kg) of the teacher is:
- A76.5
- B75.5
- C72.5
- D74.5
Solution & Step-by-step Explanation
Method 1: Total Weight Method
Total weight of 30 students = 30×60=1800kg
When the class teacher is included, total number of people = 30+1=31
New average weight = 60+0.5=60.5kg
Total weight of 31 people = 31×60.5=1875.5kg
Weight of the teacher = Total weight of 31 people − Total weight of 30 students
Weight of teacher=1875.5−1800=75.5kg
Method 2: Deviation Method
Weight of teacher=Old Average+(Total number of people×Increase in average)
Weight of teacher=60+(31×0.5)=60+15.5=75.5kg
Total weight of 30 students = 30×60=1800kg
When the class teacher is included, total number of people = 30+1=31
New average weight = 60+0.5=60.5kg
Total weight of 31 people = 31×60.5=1875.5kg
Weight of the teacher = Total weight of 31 people − Total weight of 30 students
Weight of teacher=1875.5−1800=75.5kg
Method 2: Deviation Method
Weight of teacher=Old Average+(Total number of people×Increase in average)
Weight of teacher=60+(31×0.5)=60+15.5=75.5kg