Nightlong Hints

How to solve the equation

  • 1 of 10: The laboratory door access code:
    (1) you know that this code is 446677
    (2) the symbols for this code don't appear on the blackboard
    (3) the numbers 4, 6 and 7 are excluded from the equation
  • 2 of 10: The equation can be divided into two parts:
    PART ONE: abc x dc = defc
    PART TWO: defc + cbfc = agecb
  • 3 of 10: From PART TWO:
    defc + cbfc = agecb
    "agecb" is a number in the "ten thousands"
    "agecb" cannot be 20 000 or greater
    "agecb" must be a number between 10 000 and 20 000
    therefore a=1
  • 4 of 10: From PART ONE:
    abc x dc = defc
    "c"' is the last digit in all the numbers
    so:  c x c = c (or a number ending in "c")
    therefore "c" can only be 0,1,5 or 6
    but "c" cannot be 1 (a=1) nor 6 (excluded)
    therefore "c" can only be 0 or 5
  • 5 of 10: Back to PART TWO:
    defc + cbfc = agecb
    again look at the last digit in the numbers
    so: c + c = b (or a number ending in "b")
    but "c" cannot be 0 (0 + 0 = 0 doesn't fit)
    therefore c=5
    also if: 5 + 5 = 10 (c + c = b)
    then b=0
  • 6 of 10: Staying with PART TWO:
    defc + cbfc = agecb (def5 + 50f5 = 1ge50)
    look at the last two digits in the numbers
    so: f5 + f5 = 50  (or a number ending in "50")
    therefore "f" can only be 2 or 7
    but "f" cannot be 7 (excluded)
    therefore f=2
  • 7 of 10: What do you know so far?
    a=1   b=0   c=5   f=2
    missing letters are "d", "e" and "g"
    missing numbers are 3, 8 and 9
  • 8 of 10: From PART ONE:
    abc x dc = defc (105 x d5 = de25)
    and using "trial and error":
    if "d" is 3: 105 x 35 = 3e25
    but 105 x 35 = 3675, so "d" cannot be 3
    if "d" is 9: 105 x 95 = 9e25
    but 105 x 95 = 9975, so "d" cannot be 9
    if "d" is 8: 105 x 85 = 8e25
    but 105 x 85 = 8925, so "d" can only be 8
    therefore d=8 and e=9
    also by process of elimination g=3
  • 9 of 10: The governor's door access code from the piece of paper from Eva is "e c d g f b"
  • 10 of 10: Therefore the code is  9 5 8 3 2 0.  Congratulations!