Average weight

if the average weight decreased by 3 kg, then the total of their weights decreases by 10*3=30 kg. the new person who got replaced must weigh 80-30= 50 kgs.

Let x = average weight of 10 men y = weight of other men z = weight of the new person 10 = number of men in the group 3 = kgs less from x when z came in

x=(y+80)/10=x+3

x-3=(y+z)/10

(y+80)/10 = x --> y=10x-80

10x-80=x+3 will solve x

After solving x, solve for y in y=10x-80

With x and y solved we can now solve for z in the equation (y+z)/10=x-3

let the weights be a b c d e f g h i and 80.

Then

(a + b + c + d + e + f + g + h + i + 80) / 10 = A

(a + b + c + d + e + f + g + h + i + 80) = 10 A -------(i)

Let the new person's weight be j

Then

(a + b + c + d + e + f + g + h + i + j) / 10 = A - 3

(a + b + c + d + e + f + g + h + i + j) = 10A - 30

(a + b + c + d + e + f + g + h + i + j + 30) = 10A--------------(ii)

Equation i and ii are equal because the L.H.S = 10A

a + b + c + d + e + f + g + h + i + 80 = a + b + c + d + e + f + g + h + i + j + 30

80 = j + 30

j = 80 - 30 = 50

So, the weight of the new person = j = 50 kg

let average weigt of 10 men=x/10,

replacing a person weighing 80kg by a person weighing y kgs=decreasing average weight by 3

i.e., (x-80+y)/10=x/10-3

x+y-80=x-30

y=50!!!!!!

Let x = average of the 10 men, so their total weight is 10x. If y = the weight of the new person, the new total weight is 10x - 80 + y. The new average is x - 3, so 10x -80 + y = 10(x - 3) = 10x - 30. Solving for y, y = 50. Ed Gray