Send More Money Puzzle
ADDITION is an imposition,
SUBTRACTION is as bad,
MULTIPLICATION is a vexation,
In each puzzle every letter represents a different digit, but a letter does not necessarily stand for the same digit in the case of very puzzle. Additionally, note that the leading digits are not zero.
These puzzles were created by Henry E. Dudeney in 19241. This page has solutions for each.
Addition is an imposition
Given that the sum has one more digit than the summands, it’s reasonable that must be as the result of a carry.
Notate possible carries as :
(Do not confuse the letter with )
Given that the leading digit was the result of a carry, we can be sure that:
Which gives a few branches to follow:
If and , then and , which contradicts making this branch invalid.
Next, if and then and . Following this to the next pair of digits being added, we see:
So it must be that , which would make and which contradicts making this branch invalid.
Exhausting other options, we are sure that , and
Following this to the next pair of digits being added, we see:
Given that it must be that . So:
Following to the next pair of digits be added, we see:
Solving with the previous equation, we see that
Given that (and therefor ) we know and
Looking at the final pair of digits, the following is true:
We can carve away at the bounds of by using the values of the known variables we know:
Any combination where is naturally invalid as the sum is less than . Constrain bounds:
Enumerate possibilities
Of theses (1) and (5) are invalid as . Furthermore (3) and (6) are invalid because . Finally (2) and (3) are invalid because the sum is out of bounds. This leaves:
Thus
Subtraction is as bad
Compared with the other two, I consider this problem lousy. The other problems have just one solution, whereas this one has twenty. With how many solutions exist, I’d say the best manual strategy is to guess and check. Instead, I wrote a python program2 to find all solutions.
View Code
def digits(n):
dig = []
while n > 0:
dig.append(n % 10)
n //= 10
return list(reversed(dig))
for a in range(10000, 99999):
for b in range(1000, 9999):
if not (1000 <= a-b <= 9999):
continue
[E, I, G, H, T] = digits(a)
[F, I_2, V, E_2] = digits(b)
[F_2, O, U, R] = digits(a-b)
if I != I_2 or E != E_2 or F != F_2:
continue
unique = [E, I, G, H, T, F, V, O, U, R]
if len(set(unique)) != len(unique):
continue
print(a, b)
View all solutions
12348 - 6251 = 6097
12348 - 6291 = 6057
12375 - 6281 = 6094
12375 - 6291 = 6084
12780 - 6231 = 6549
12780 - 6241 = 6539
14820 - 7451 = 7369
14820 - 7461 = 7359
15230 - 7541 = 7689
15230 - 7581 = 7649
16725 - 8631 = 8094
16725 - 8691 = 8034
16743 - 8651 = 8092
16743 - 8691 = 8052
16905 - 8631 = 8274
16905 - 8671 = 8234
17036 - 8741 = 8295
17036 - 8791 = 8245
17054 - 8761 = 8293
17054 - 8791 = 8263
Multiplication is a vexation
For convenience:
First, note that the result has exactly five digits. The largest 5-digit square is and the smallest is Notate constraints
We can further constrain the bounds by noticing that the first digits of are shared as .
The first-digit constraint can only be true when and
Now, notice how the digit is determined only by the value of the square of .
Find squares of digits
Meaning must be one of those square digits
Let’s now focus on the last two digits, which are determined only by the value of . Expand:
We can ignore the 100s term as we’re only focusing on the last two digits.
Now, we’ve already determined that and are constrained to certain values. Try each possibility
Possibilities where and share digits are naturally invalid and can be removed.
We use these possibilities in the equation found above to determine
Try :
This equation has solutions at . We can ignore as we have already determined . Looking at we see which is out of bounds; .
As all branches are dead ends, we are sure that
Instead, try :
Which has no solutions. Dead end.
Instead, try :
Which has no solutions. Dead end.
Instead, try :
Which has no solutions. Dead end.
Therefor, by elimination
Which has one valid solution, . Substitute in known digits
Naturally, the remaining digits are found within
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The Strand Magazine, July 1924 edition. Page 97. Henry E. Dudeney (view online).
Note that a fourth puzzle on division is found in the original source. I have excluded this puzzle as I couldn’t properly typeset it. ↩︎ -
It’s very inefficient. I know. ↩︎