Question

5.
1 Se stie ca a+b=21. Calculati 100a+100b.
2 Se stie ca a +b+c+9.Calculati 5a+5b+5c
3 stiind ca a+3b=12 si b+c+4, calculati 2a+9b+3c

Answer 1

1) a+b=21 ⇔ a=21-b
100a+100b= 100(21-b)+100b= 2100-100b+100b=2100
2) a+b+c=9 ⇔ a=9-b-c
5a+5b+5c= 5(9-b-c)+5b+5c= 45-5b-5c+5b+5c= 45
2) a+3b=12 ⇔ a=12-3b
    b+c=4 ⇔ b=4-c
2a+9b+3c = 2(12-3b) + 9(4-c) + 3c = 2(12-3[4-c]) + 9(4-c) + 3c = 2(12-12+3c)+9(4-c)+3c= 6c+36-9c+3c = 36