Question

The average weight of a class of 20 students is 45kgs. A new student whose weight is 40kgs replaced an old student of this class. The average weight of the whole class decreases by 1 kg. The weight of the replaced student is

Answer 1

Answer:

60

Step-by-step explanation:

Given average weight of whole class decreases by 1 kg, thus on a whole since there are 20 students , the net weight decrement is 20*1 = 20 and since a new student weight is 40kgs , therefore replaced student weight should be 40 + 20 = 60kgs.

Aliter:

Let weights of the students are w₁, w₂,......,w₂₀ and let w₂₀ be the weight of the student whose weight is replaced.

A₁ = (w₁+w₂+.....w₁₉+w₂₀)/20 =45

A₂ = (w₁+w₂+.....w₁₉+40)/20 = 44

A₁-A₂ gives (w₂₀-40)/20 = 1,

Thus w₂₀ = 60.

Answer 2

Answer:

old student weight = 60kgs

Step-by-step explanation:

Let 'w' be the weight of old student

It is given that,the average weight of a class of 20 students is 45kgs

Therefore total weight = 20 x 45 = 900

New student whose weight is 40kgs

If new student replace old student the average weight reduced by 1 kg.

That is average weight = 44

The total weight after arrival of new student = 44 x 20 = 880

To find the weight of old student

$\frac{900+40-w}{20}=880$

940 - w = 880

w = 60

Therefore old student weight = 60kgs