Posted:

**Mon Mar 07, 2005 7:09 pm**I'm a bit confused about what you are asking, but 2:7 is the wrong answer.

What you are doing is diluting a dilution. The first dilution is 25% (1 part developer + 3 parts water). The second dilution is 20% of the first dilution (1 part stock solution + 4 parts water). My math isn't perfect and maybe someone will correct this, but I calculate the total working solution to be 5% strength.

If you think about it in real terms it might be easier. Say you mix 25ml developer with 75ml water (1+3) to make 100ml stock. Then you mix the 100ml of the stock solution with 400ml of water (1+4) to make a total of 500ml working solution. The total amount of concentrate in 500ml of working solution is 25ml, or 5%. This works out to 1+19.

If anyone can explain this in purely mathematical terms (how to calculate 1+3 dlluted 1+4) then please post a response.

What you are doing is diluting a dilution. The first dilution is 25% (1 part developer + 3 parts water). The second dilution is 20% of the first dilution (1 part stock solution + 4 parts water). My math isn't perfect and maybe someone will correct this, but I calculate the total working solution to be 5% strength.

If you think about it in real terms it might be easier. Say you mix 25ml developer with 75ml water (1+3) to make 100ml stock. Then you mix the 100ml of the stock solution with 400ml of water (1+4) to make a total of 500ml working solution. The total amount of concentrate in 500ml of working solution is 25ml, or 5%. This works out to 1+19.

If anyone can explain this in purely mathematical terms (how to calculate 1+3 dlluted 1+4) then please post a response.