Question

已知x/3=y/4=z/5，且2x+y-z=21，则3x+y+z=

Answer 1

解：设x/3=y/4=z/5=k
∴x=3k,y=4k,z=5k
∴2x+y-z=6k+4k-5k=5k=21
∴k=21/5
∴3x+y+z=9k+4k+5k=18k=378/5

Answer 2

因为:X/3=Y/4=Z/5
得出:Y=4X/3,和Z=5X/3
代入:2X+Y-Z=21中
得:2X+4X/3-5X/3=21
解得:X=12.6
将X=12.6代入Y=4X/3,Z=5X/3中
解得Y=16.8,Z=21
所以3X+Y+Z=3*12.6+16.8+21=75.6
这是最基本的解法.

Answer 3

设X/3=Y/4=Z/5=A,那么x=3A,Y=4A,Z=5A,而且2X+Y--Z=6A+4A-5A=21,那么A=4.2 3X+Y+Z=12.6*3+16.8+21=75.6