Question

the average weight of a class of 40 boys is 55 kg the average weight is raised to 56 kg. if the weight of teacher is added then the weight of the teacher in kg. is

Answer 1

Total Boys=40
AVERAGe weight=55 kg

Now weight Of all 40 boys will be different.
Like one have 36 kg then other may be 68.
We had not known.But average of all is 55kg

Let Actual sum of weight of all student.
=a1+a2+a3__.._..__a40.
Now Total student=40

AVERAGe=Sum/Total Numbers
a1+a2+a3.........A40/40=55
a1+a2+a3......+a40=55×40
a1+a2+a3.....+a40=2200
40 Student weight SUM=2200 KG

Now Teacher had join
Then total people=41
Actual weight=a1+a2+a3.....a40+a41
AVERAGe=56

Now
40 Student weight=2200 kg
So,
a1+a2+a3....+a40+a41/41=56
2200+a41/41=56
2200+a41=56×41
2200+a41=2296
a41=2296-2200
a41=96

So Teacher Weight=96 kg

Answer 2

Average weight of boys= 55 kg
Total boys = 40
so,The total sum of weight of boys=40*55
=2200kg
when teacher is added,
Average weight = 56kg
Total persons=40 boys+1 teacher=41
Sum of total weight =41*56
=2296kg
so, weight of teacher =(2296-2200)kg
=96kg ans..