???????????????????????????????

3)
a |-----|+7|
b |-----| } 3971.
3971 - 7 = 3964 ( 2 segmente egale)
3964 : 2 = 1982 (b)
1982 + 7 = 1989 (a)
Verificare : 1989 + 1982 = 3971 ( suma )
1989 - 1982 = 7 ( diferenta)
4)
2005 + 2437 = 4442
sau :
2005 +
2437
---------
4442
5)
Numerele de forma " aa " sunt nr care au aceleasi cifre.
11 + 22 + 33 + 44 + 55 + 66 + 77 + 88 + 99 = 495
Suma tuturor nr naturale de forma " aa " este 495.
3.
a+b=3971 \\ \\ a-b=7=>a=b+7 \\ \\ b+7+b=3971 \\ 2b+7=3971 \\ 2b=3964 \\ b=3964:2 \\ b=1982 \\ \\ a=1982+7 \\ a=19890
4.
2437+2005=4442
5.
Nr. de forma aa sunt 11,22,33,44,55,66.77,88,99
11+22+33=44+55+66+77+88+99=495