Ta có: `3a=4b=5c` và `a.b.c= 27/60`
Ta có: BCNN`(3,4,5)=60`
=>`(3a)/60 = (4b)/60 =(5c)/60`
=> `a/20 =b/15= c/12` và `a.b,c= 27/60`
Ta có: `a/20 =b/15= c/12=k`
Ta có: `a=k.20` `b=k.15` `c=k.12`
Ta có: `a.b.c= 27/60`
`k.20.k.15.k.12= 27/60`
`k^3 .(20.15.12)= 27/60`
`k^3 . 3600=27/60`
`k^3 .3600= 9/20`
`k^3 =9/20 :3600`
`k^3= 1/8000`
`k= 1/20`
=> `a/20=1/20⇒a.20=20.1`
` a.20=20`
`a=20:20`
`a=1`
=> `b/15=1/20⇒b.20=15.1`
`b.20=15`
`b=15:20`
`b=3/4`
=> `c/12=1/20⇒c.20=12.1`
`c.20=12`
`c=12 :20`
`c=3/5`
Ta có: `a+b+c=1 +3/4 +3/5=20/20+15/20 +12/20=47/20`
Vậy `a+b+c=47/20`
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