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Determinati numerele x,y,z invers proportionale cu 2,5,20 iar a+b+c=60

Răspuns :

2x=5y=20z=k
x=k/2
y=k/5
z=k/20
x+y+z=60
k/2 + k/5 + k/20=60
Aducem la numitor comun, 20.
10k+4k+k=1200
15k=1200 =>k=80
=>x=40
=>y=16
=>z=  4
Notam
x·2=y·5=z·20=k
x=k/2
y=k/5
z=k/20
x+y+z=60 ⇔
k/2+k/5+k/20=60 ⇔
10k+4k+k=20·60 ⇔
15k=1200 ⇔
k=80
x=40
y=16
z=4