Te salut, Seby!
Răspuns: a = 11
Explicație pas cu pas:
12 + [ 32 : 8 + 2 x ( 3 x 5 – a ) – 12 : 2 ] : 2 = 15
[ 4 + 2 x ( 15 – a ) – 6 ] : 2 = 15 - 12
[ 4 + 2 x ( 15 – a ) – 6 ] : 2 = 3
4 + 2 x ( 15 – a ) – 6 = 3 × 2
4 + 2 x ( 15 – a ) – 6 = 6
4 + 2 x ( 15 – a ) = 6 + 6
4 + 2 x ( 15 – a ) = 12
2 x ( 15 – a ) = 12 - 4
2 x ( 15 – a ) = 8
15 – a = 8 : 2
15 – a = 4
a = 15 - 4
a = 11 → numărul, aflat prin metoda mersului invers
Verific:
12 + [ 32 : 8 + 2 x ( 3 x 5 – 11 ) – 12 : 2 ] : 2 = 15
= 12 + ( 4 + 2 × 4 - 6 ) : 2 =
= 12 + 6 : 2 =
= 12 + 3 =
= 15
