LOL sorry i just woke up too ignore "they". Concentration percentage of mass-volume is Weight divide by Volume x100% so 1g/100ml(H2O) *100% is 1% solution like 1 gram of sucrose divide by 100ml of water time 100% is a 1% sucrose solution or in your case 1% sodium thiosulfate is (1g Na2S2O3/100ml H20*100%). You stat you want 32% of sodium thiosulfate which is (32g/100ml *100%). You stat you want to make 1/2 liter which is 500 ml and you want to get the mass of sodium thiosulfate so to do that we did (32g Na2S2O3/100ml *500ml)=160g Na2S2O3. Now (160g/500ml *100%) give us 32%. To make extremely it precise add 160g first then fill it up to 500ml mark with distill water. If there any confusion just ask.