If measurements if a gas are 75l and 300 full-scale and then the gas is measured a second time and found to be 50l, describe what had to happen to the pressure (if temperature remained constant).

The answer is a bit confusing, so I did some research and fount the original question. This is the complete question:

"If measurements of a gas are 75L and 300 kilopascals and then the gas is measured a second time and found to be 50L, describe what had to happen to the pressure (if temperature remained constant). Include which law supports this observation".

From that:

1) Data:

V1 = 75 liter
P1 = 300 kPa

V2 = 50 liter
P2 = x

T = constant.

2) Analysis (physical law)

Boyle's law states that the volume of a fixed amount of gas, at constant temperarature, is inversely related with the pressure.

In mathematical form that statement becomes into this equation:

PV = constant (at constant T)

=> P1V1 = P2V2.

Then, the decreasing of the volumen (compression) is accompanied by an increase of the pressure.

3) So, using Boyle's law with the data given:

300 kPa * 75 liter = x * 50 liter

=> x = 300 kPa * 75 liter / 50 liter = 450 kPa.

following Boyle's law, when the gas passed from 75 liter to 50 liter the pressure had to increase from 300 kPa to 450 kPa.

The independent variable would be the fertilizer as it is what the dependent variable (the growth of grass) depends on.