Use the dilution calculation formula and remember to make the units match.

C1V1=C2V2

Your question is incomplete. You haven't mentioned the final volume.

Hi Noimul Hasan Siddiquee ,

Given: 1 µM (µMolar) = 1 pmol/µl (pico moles/µl)

Given: Ci x Vi = Cf x Vf

I guess your stock solution is 100 µM = 100 pmol/µl and your working solution is 10 µM = 10 pmol/µl.

So, for a volume of 5 µl of primer of 100 µM, you have to add 45µl of water to have a 50µl volume of primer of 10 µM.

Noimul Hasan Siddiquee you should double check if you really mean picoM (a concentration) or pico moles. PicoM concentration (pico moles per liter) would be vanishing small (about a million fold dilution) but I think that is what you wrote. If you mean pico moles per microliter then see above.

I think you have the wrong question.

It should be how much 100 uM primer should I add to get 10 pMol.

The first is the concentration of the primer. The second is the actual number of molecules you want to add to the reaction mix. !00 uM is uMoles per liter volume in terms of concentration. 10 pMol is the number of molecules per reaction mix. 10 pMol is a common amount to be added.