Question

1/5 dintr-un nr este cat 1/2 din altul.Aflati nr stiind ca au media aritmetica 140.

Answer 1

1/5·a=1/2·b⇒a/5=b/2⇒
2a=5b⇒a=5b/2
Media aritmetica=(a+b)/2 inlocuim
140=(5b/2+b)/2⇒aducem la acelasim numitor paranteza⇒
7b/2:2/1=140
7b/2·1/2=140
7b/4=140
7b=140·4
b=560/7
b=80
a=5b/2=5·80/2
a=200
verificare
media aritmetica=80+200/2=280/2=140

Answer 2

(1/5)x=(1/2)y

(x+y)/2=140       ⇒x+y=280  si 2x=5y ⇒ x=280-y  :   2(280-y)=5y  

560-2y=5y  ⇒7y=560  

y=80

x=280-y  ⇒x=200