how much silt do you need to add to 4ft cube of soil with 10% silt in order to make a soil with 60% silt?
4 cubic ft (cf) of soil contains
4*10%=0.4 cf of silt
If we add x cf of silt,
total volume = 4+x
volume of silt = 0.4+x
Given the new percentage is 60%, we have
(0.4+x)/(4+x)=0.6
Solve for x by cross multiplication:
0.4+x = 0.6(4+x)=2.4+0.6x
transpose and solve for x
x-0.6x=2.4-0.4
0.4x=2.0
x=5
Check:
(0.4+5)/(4+5)=5.4/9=0.6=60% √