a)

1 + 2 + 3 + 4 + 5 + 6 + 7 + (8 x 9) = 100
(1 + 2 + 3 + 4 + 5 ) 6 + 7 + 8 + 9 = 100
1 + 2 x 3 + 4 + 5 + 67 + 8 + 9 = 100
1 + 2 + 3 + 4 + 5 + 6 + 7 + 98 = 100
(1 + 2 + 3 + 4 + 5 ) x 6 + 7 + 8 + 9 = 100
- (1 x 2) - 3 - 4 - 5 + (6 x 7) + (8 x 9) = 100
1 + (2 x 3) + (4 x 5) - 6 + 7 + (8 x 9) = 100
(1 + 2 - 3 - 4) (5 - 6 - 7 - 8 - 9) = 100
(1 x 2) + 34 + 56 + 7 - 8 + 9 = 100

b)

(9 + 8 + 7 + 6 - 5) x (4 + 3 + 2 +1) = 100
(9 x 8) + 7 + 6 + 5 + 4 + 3 + 2 + 1 = 100
(9 x 8) + 7+ 6 + 5 + (4 x 3) - (2 x 1) = 100
(9 x 8) + 7 + (6 x 5) - (4 x 3) + 2 + 1 = 100
(9 x 8) + 7 - 6 + (5 x 4) + (3 x 2) + 1 = 100
(9 x 8) + (7 x 6) - 5 - 4 - 3 - (2 x 1) = 100
(- 9 - 8 - 7 - 6 + 5) (- 4 - 3 + 2 + 1) = 100

c)

1 + 2 + 34 + 5 + 67 + 8 + 9 = 100
1 + 23 + 4 + 56 + 7 + 8 + 9 = 100
12 + 3 + 4 + 5 + 6 + 7 + 89 = 100
1 + 2 + 3 + 4 + 5 + 6 + 7 + (8 x 9) = 100
123 - 4 - 5 - 6 - 7 + 8 - 9 = 100
123 - 45 - 67 + 89 = 100
123 + 45 - 67 + 8 - 9 = 100
123 + 4 - 5 + 67 - 89 = 100
1 + 23 - 4 + 5 + 6 + 78 - 9 = 100
12 + 3 - 4 + 5 + 67 + 8 + 9 = 100
1 + 2 + 3 - 4 + 5 + 6 + 78 + 9 = 100 

d)

9 + 8 + 76 + 54 + 32 + 1 = 100
98 + 7 + 6 + 5 + 4 + 3 + 2 - 1 = 100
98 + 7 + 6 + 5 + 4 + 3 + 2 + 1 = 100
98 - 76 + 54 + 3 + 21 = 100
98 - 7 - 6 - 5 - 4 + 3 + 21 = 100
98 - 7 + 6 + 5 + 4 - 3 - 2 - 1 = 100
98 + 7 + 6 - 5 - 4 - 3 + 2 - 1 = 100
98 + 7 - 6 + 5 - 4 - 3 + 2 + 1 = 100
98 - 7 + 6 + 5 - 4 + 3 - 2 + 1 = 100
98 - 7 + 6 - 5 + 4 + 3 + 2 - 1 = 100
98 + 7 - 6 - 5 + 4 + 3 - 2 + 1 = 100
9 + 8 + 76 + 5 + 4 - 3 + 2 - 1 = 100
9 + 8 + 76 + 5 - 4 + 3 + 2 + 1 = 100

    "si digo como solución 1+2*3, me estaré refiriendo a (1+2)*3, es decir, siempre el primer número con el segundo, este con el siguiente..."

a)

b)

c)

123-4-5-6-7+8-9
123+4-5+67-89
123+45-67+8-9
123-45-67+89

d)

9+8+76+6+5-4+3-2-1
9+8+76+6+5-4-3+2+1
9+8+76+6-5+4+3-2+1
9+8+76-6+5+4+3+2-1