Răspuns :
a+c=10 10a+10c=10×10=100
a+b=8 5a+5b=8×5=40
15a+5b+10c=100+40
=140
a+b=8 5a+5b=8×5=40
15a+5b+10c=100+40
=140
a + c = 10 si a + b = 8
15 a + 5 b + 10 c = 140
= 10 a + 10 c + 5 a + 5 b =
= 10 × ( a + c ) + 5 × ( a + b ) =
= 10 × 10 + 5 × 8 =
= 100 + 40 =
= 140