Răspuns:
Explicație pas cu pas:
[ ( 420 : a ) × 4 + 24 ] : 4 = 11
( 420 : a ) × 4 + 24 = 11 × 4
( 420 : a ) × 4 + 24 = 44
( 420 : a ) × 4 = 44 - 24
( 420 : a ) × 4 = 20
420 : a = 20 : 4
420 : a = 5
a = 420 : 5
a = 84 => numarul, aflat prin metoda mersului invers
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Verific:
[ ( 420 : 84 ) × 4 + 24 ] : 4 = ( 5 × 4 + 24 ) : 4 = 44 : 4 = 11