Question

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

Solution:

Given that, From 1980 to 1990, Lior’s weight increased by 25%

The percentage increase is given by formula:

$\text{Percent increase } = \frac{\text{final value - initial value}}{\text{ Initial value}} \times 100$

From given,

Percent increase = 25 %

Final value in 1990 = "k" kilograms

Initial value in 1980 = ?

Let "x" be the initial value in 1980

Substituting the values in formula, we get,

$25 = \frac{k- x}{x} \times 100\\\\25x = 100(k-x)\\\\Divide\ both\ sides\ of\ equation\ by\ 25\\\\x = 4(k-x)\\\\x = 4k - 4x\\\\x + 4x = 4k\\\\5x = 4k\\\\x = \frac{4}{5}k$

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