Not possible, unless you evaporate most of water.  Each ml of water is 1 g.  If you dissolve 10g substance in 10 ml of water (i.e., 10 g water), you have 50% by weight, 50% weight is substance, 50% is water.

1000 ml water is 1000 g.  If you put the 10 g in the liter of water, your percentage by weight is 10g/1010g

The 10 g substance in 40 ml water is 20% by weight.  10 g substance in 15 ml water is the 40%.  

Hi Umar,

I guess you are trying to obtain a dissolution serie.  So if this is your goal, you can use a dilution factor method.   

if         C1= concentration 1  ^  C2 = concentration 2

and      V1=  Initial Volumen   ^ V2 = final volumen

for:

 C1*V1 = C2*V2

Then

C2= (C1*V1)/ V2

Lets say, that you want to prepare 200 mL at 40% from your initial concentration 10g /L (100%):

V1= (250 mL)*(40%) / (100%)

V1= 100mL

This means, that you need to take 100 mL of your original dissolution and add to it 150 mL of des Water to obtain a final concentration of 40% (mass/volume).

 Hope it help, 

best regards,

Mario 

Plesae find attached a quick procedure for dissolutions preparation (source= http://www.mgel.msstate.edu/pdf/solutions.pdf)

OK, Mario assumed you already had 10g in 1 liter water.  I did not gather that in my reading you initial question.  Perhaps that is your stock solution, and it's concentration is 10000 mg/l.  You mix it once, and then use it to mix other concentrations or standards.  If you are mixing dilution standards, Marios equations are correct, and with practice, you can do them in your head, or they just make sense to you.  If I want a 50% dilution of my stock, i.e., 5000 mg/l is the desired concentration and want to mix it in a 100 ml volumetric flask, take 50 ml of the stock, and 50 ml of distilled water.  Let's say I want a standard of 100 mg/l.  If I use a 100 ml volumetric flask, I must carefully pipette in 1ml and fill to 100 ml line.  If you are not really steady, a drop or two might come out in the transfer.  So you might decide to use a 1000 ml volumetric flask and pipette in 10 ml.  Both ways is a 100 fold dilution of the stock.  Whether you are using the equations or doing dilutions in your head, check yourself.  Pipette and mixing standard  solutions is meticulous work.  If you see an air gap at the bottom of the filled pipette, a drop or two jiggled out, so redraw the fluid to keep accuracy, i.e. Filled to proper line to bottom of maniscus and no air gap.  There is a rubberized bulb tool you can purchase to assist in filling and draining pipettes, avoid contact with hazardous or questionable substances that is probably easier, otherwise fill to above line and drain to mark.  Avoid sucking liquids into bulb, that may ruin it unless you can get all fluids out.  If you know a person running a water quality testing lab, they are used to this and may provide added help, show how to clean glassware, sterilize if needed, label dilutions with marking pen and date, storage, etc.