a,b,c sunt trei nr naturale. stiind ca a+b=7 si b+c+10, calculati 3*a+5*b+2*c

Răspuns :

b = 10-c → a = 7-b = 7 - (10-c) = c+3; 3(c+3) + 5(10-c) + 2c = 3c+9+50-5c+2c = 59. Deci 3a+5b+2c = 59.

a+b=7

b+c=10

5•b=3•b+2•b

3•a+5•b+2•c=

3•a+3•b+2•b+2•c=

3(a+b)+2(b+c)=

3•7+2×10=

21+20=

41