Insert only THREE arithmetical operators between the digits on the left, so an equality follows.

For example, you could try 123x456+78/9... but somehow it doesn't work!

 123 - 45 - 67 + 89

from

DEFDBL A-Z
s$ = "123456789"
ops$ = "*/+-"
FOR p1 = 1 TO 6
FOR p2 = p1 + 1 TO 7
FOR p3 = p2 + 1 TO 8

  n1 = VAL(MID$(s$, 1, p1))
  n2 = VAL(MID$(s$, p1 + 1, p2 - p1))
  n3 = VAL(MID$(s$, p2 + 1, p3 - p2))
  n4 = VAL(MID$(s$, p3 + 1, 9 - p3))
  FOR op1 = 1 TO 4
  FOR op2 = 1 TO 4
  FOR op3 = 1 TO 4

    op(1) = op1
    op(2) = op2
    op(3) = op3
    n(1) = n1
    n(2) = n2
    n(3) = n3
    n(4) = n4
    FOR i = 1 TO 3
      IF op(i) = 1 OR op(i) = 2 THEN
        IF op(i) = 1 THEN
         n(i + 1) = n(i + 1) * n(i)
        ELSE
         n(i + 1) = n(i) / n(i + 1)
        END IF
        op(i) = 0
        n(i) = 0
      END IF
    NEXT i
    FOR i = 1 TO 3
      IF op(i) = 3 OR op(i) = 4 THEN
        j = i + 1
        DO WHILE j < 3 AND op(j) = 0
          j = j + 1
        LOOP
        IF op(i) = 3 THEN
         n(j) = n(j) + n(i)
        ELSE
         n(j) = n(i) - n(j)
        END IF
        op(i) = 0
        n(i) = 0
      END IF
    NEXT i
    t = n(4)
    IF ABS(t - 100) < 1E-12 THEN
      PRINT n1; MID$(ops$, op1, 1);
      PRINT n2; MID$(ops$, op2, 1);
      PRINT n3; MID$(ops$, op3, 1);
      PRINT n4
    END IF

  NEXT
  NEXT
  NEXT

NEXT
NEXT
NEXT