Question

PLEASE HELP/ANSWER! From 1980 to 1990, Lior’s weight increased by 25%. If his weight was k kilograms in 1990, what was it in 1980?

Answer 1

The weight in 1980 is $\frac{4k}{5}$ 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:

$\text{Percentage increase } = \frac{\text{Final value - initial value}}{\text{initial value}} \times 100$

Here,

Initial value in 1980 = x

Final value in 1990 = k

Percentage increase = 25 %

Substituting the values in formula,

$25 = \frac{k-x}{x} \times 100\\\\25x = 100(k-x)\\\\x = 4(k-x)\\\\x = 4k - 4x\\\\5x = 4k\\\\x = \frac{4k}{5}$

Thus the weight in kilograms in 1980 is $\frac{4k}{5}$