How do make 10gm/Lt. solution from from 100gm/Lt. stock solution?

Let's do this 2 different ways

(1)  You have 100gm in a 1000ml so you must have 10gm in 100ml

So if you take 100ml of the strong solution it will contain 10mg.  So you just need to add 900ml of the solvent (probably water)

then you will have 10mg in 1 litre which is what you want.

(2) There is a nursing 'formula' for this it says

The amount of strong soln needed =  $$\begin{array}{rll} \mbox{the amount of strong solution needed}&=&\frac{\mbox{concentration required}}{\mbox{concentration available}}\times \mbox{ total quantity required}\\\\ &=&\frac{10g/L}{100g/L}\times 1000mL\\\\ &=&\frac{1}{10}\times 1000mL\\\\ &=&100ml \qquad \mbox{of strong solution is needed}\\\\ \end{array} \mbox{The rest is solvent}\\\\ 1000mL-100mL=900mL\; of\; solvent\;is\;also\;added\; (Water)$$