No. If I read you clearly what you have now is a 120ml bottle of PG which contains 10% nicotine (100 mg per ml)
Yes. adding 130 ml of zero nicotine to your 120ml of 100mg nic pg will result in 250ml of base containing 48mg per ml.
Well...no...
To end up with 250 ml of 50%PG x 50%VG x 48mg nicotine base solution you would have to add 5ml of plain pg and 125ml of plain vg
This 48mg base you would plug into an e-juice calculator to be further diluted with your flavorings plus more pg and/or vg to arrive at your target mg strength for vaping and you would also use the mixing calculator to give you your target pg/vg ratio. The pg/vg ratio is arrived at based on how much flavorings are in your mix (usually flavorings are in a pg carrier but not always) and thus the final pg/vg ratio adjustment can usually be made in the amounts of plain pg and vg that gets added into the calculated final mix.
I would suggest using one of the calculators at
Do It Yourself E-Liquid (E-Juice) Recipe Mixing Station! which are very accurate for safely calculating your target nicotine strength as well as your target pg/vg ratio adjustment.
There are several other great calculators out there you can download for use offline as well as some online like the ecigvape ones.
One very popular calc program is the "e-juice me up" program. Several others are spreadsheet based and also work quite well.
semi off topic rant....
The one calculator I would NOT trust UNTIL THEY FIX IT.... is the one at diyrecipebook dot com as its pg/vg ratio is waaayyyy off especially if you try to adjuast the target ratio using the slider bar on their calculator. It's all over the place and seldom correct ime. I'm sorry I have to mention it online, but I havent seen them fixing it yet so perhaps when more people are aware they might wake up and finally fix it. Their site itself is really very nice as a recipe book goes, its just a bummer that its calc is broken at this point in time. otherwise i do love everything else about it fwiw.
hth, good luck and happy vaping