a) 107 × 43 + 107 × 56 + 107 =
107 × ( 43 + 56 + 1 ) =
107 × ( 99 + 1 ) =
107 × 100 = 10700
b) 46 × 39 + 46 × 47 + 86 × 32 + 86 × 23 =
46 × ( 39 + 47 ) + 86 × ( 32 + 23 ) =
46 × 86 + 86 × 55 =
86 × ( 46 + 55 ) =
86 × 101 = 8686
c) 2 + 4 + 6 + ... + 20 =
2 × ( 10 × 11 : 2 ) =
2 × ( 110 : 2 ) =
2 × 55 = 110