已知x+y=3,y+z=4,x+z=5,则x+y+z等于(  ) A.6 B.8 C.10 D.12

问题描述:

已知x+y=3,y+z=4,x+z=5,则x+y+z等于(  )
A. 6
B. 8
C. 10
D. 12

由题意得:

x+y=3①
y+z=4②
x+z=5③

①+②+③得:2x+2y+2z=12,
即x+y+z=5.
故选A.