Răspuns:
Explicație pas cu pas:
( 42 : 7 × 7 - 2 ) : 4 × 10 = ( 5 × 7 + 5 ) : 8 + 9 × 10 + a
( 6 × 7 - 2 ) : 4 × 10 = (35 + 5) : 8 + 90 + a
(42 - 2 ) : 4 × 10 = 40 : 8 + 90 + a
40 : 4 × 10 = 5 + 90 + a
10 × 10 = 95 + a
100 = 95 + a
a = 100 - 95
a = 5 → numarul, aflat prin metoda mersului invers
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2)
( 1 + 1 × 7 + 1 × 10 ) : ( 40 : 8 + 4 ) : a = 45 : 5 : ( 3 × 3 )
( 1 + 7 + 10) : ( 5 + 4 ) : a = 9 : 9
18 : 9 : a = 1
2 : a = 1
a = 2 : 1
a = 2
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3)
( 29 + 47 - 2 × 3 ) : ( 1 + 2 × 3 ) = ( 7 × 8 - 4 × 4 ) : a
( 76 - 6 ) : ( 1 + 6 ) = ( 56 - 16 ) : a
70 : 7 = 40 : a
10 = 40 : a
a = 40 : 10
a = 4 → numarul
