Răspuns :
( 1 × 2 × 3 ) × a = 10 × 3 × 1
( 2 × 3 × 5 ) × a = 10 × 3
( 6 ×5) × a = 30
30 × a = 30
a = 30 : 30
a = 1
( 2 × 3 × 5 ) × a = 10 × 3
( 6 ×5) × a = 30
30 × a = 30
a = 30 : 30
a = 1