gia su nA=1,5mol=> nB=3,2mol 
phuong phap duong cheo cho khi B ta tinh duoc nO2=2, nO3 =1,2 
=>nO=2*2+1,2*3=7,6 
goi cong thuc chung cua A la:CxHy 
CxHy + O -------> xCO2+y/2 H2O 
1,5 1,5x 1,5*y/2 
bao toan nguyen to O taco 
1,5*2*x + 1,5*y/2 = 7,6 
mat khac : (1,5x)/(1,5y/2)=1,3/1,2 <=> 2,4x-1,3y=0 
giai duoc x=26/15 y=16/15 
MCxHy = 12*26/15+ 16/15= 24 
=>ti khoi cua A so voi hidro la: 24/2=12