Relative Density Question

[Jambruins]

A dry sand has a minimum unit weight of 105 lb/ft and a maximum unit weight of 125 lb/ft . The unit

weight in place is measured at 121 lb/ft . What is the relative density?

The answer is 83% but how do you get this? Thanks.

 

[Marissa]

use this formula, (1-min/in-place)/(1-min/max), you'll get the answer

A dry sand has a minimum unit weight of 105 lb/ft and a maximum unit weight of 125 lb/ft . The unit
weight in place is measured at 121 lb/ft . What is the relative density?

The answer is 83% but how do you get this? Thanks.