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Smudge Sludge (Posted on 2004-04-28) Difficulty: 3 of 5
   ??7
 x 3??
  ?0?3
  ?1?
 ?5?
 ?7??3
The above equation was written on a chalkboard to represent an example of a correctly answered multiplication problem. However, the class prankster went when the teacher wasn't looking and smudged many of the numbers. What did the original problem read?

See The Solution Submitted by Gamer    
Rating: 3.6667 (3 votes)

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Solution Reasoned solution | Comment 2 of 9 |
To help understand, let's substitute letters for the question marks.

AB7
x 3CD
-----
E0F3
G1H
I5J
-----
K7LM3

7xD ends in 3, so D=9. AB7x9 must have a 0 in the second place; for B=0, 1, 2, 3, 4, 5, 6, 7, 8, 9 we find A=0, 1, 2, 3, 4, 5, 6, 6, 7, 8 (but the first possibility (A=0) isn't usually allowed).

AB7x3 must be only three digits long, so AB=11 or 22, but only 117x3 has a 5 in the second place.

Finally, 117xC must have a 1 in the second place, so C=1, and we get


117
x 319
-----
1053
117
351
-----
37323

  Posted by Federico Kereki on 2004-04-28 17:58:06
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