Question

ce cantitate de zahar trebuie adaugaa peste 200g sirop concentrat de 10% pentru a obtine 30%?

Answer 1

md1 = c1*ms1/100 = 200*10/100 = 20 g zahăr
md2 = md1 + x = 20+x
ms2 = ms1+x = 200+x
c2 = md2/ms2*100
30 = (20+x)/(200+x)*100
2000+100x=6000+30x
70x=4000
x = 57,142 g zahăr adăugat

Answer 2

c / 100 = masa dizolvata / masa solutiei 

masa dizolvata in siropul initial = md = c x masa solutiei / 100 = 10 x200: 100  =  20  grame 

soutia finala se concentreaza prin adaugarea unei mase suplimentare mx de zahar 

cfinal/100 =  (md+mx) / (msolutie + mx)

30 /100 = (20 + mx) / (200 + mx) 
30 x 200 + 30 mx = 200 x 100 + 100 mx 

6000 +30 mx = 2000+ 100 mx 
4000 = 70 mx 

mx = 4000: 70 = 57,1428 grame 

facem  proba,
md final = 20 + 57,1428 = 77,1428 
ms final  = 200 + 57,1428 = 257,1428 

c final = 100 x 77,1428 : 257,1428 = 29,99998 ≈ 30%