The weight in 1980 is
kilograms
Solution:
From 1980 to 1990, Lior’s weight increased by 25%
His weight is "k" kilograms in 1990
To find: weight in 1980
This is a percentage increase problem
Let "x" be the weight in kilograms in 1980
The percentage increase is given by formula:

Here,
Initial value in 1980 = x
Final value in 1990 = k
Percentage increase = 25 %
Substituting the values in formula,

Thus the weight in kilograms in 1980 is
