Things to write in a solution

Logic Level 4

L E M M A + C L A I M P R O O F \large{\begin{array}{ccccccc} && & L & E& M & M&A\\ +&& & C & L& A & I&M\\ \hline & & & P & R& O & O&F\\ \hline \end{array}}

Above shows a cryptarithm such that each letter represent a distinct single non-negative integers with L , C L,C and P P are non-zero. Find the value of the 6-digit number: F O R M A L \overline{FORMAL} .


The answer is 908721.

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1 solution

A A
Mar 17, 2016

Since in the 2nd and the 3th row of the addition there is that M+I->O and A+M->0 therefore for the same quantity M corresponding by addition with I and A which are distinct the same quantity it means that at least in one of the rows there is a carry and since in the first row of the addition A+M gives a different result than A+M in the third it means that there is necessarily a carry in the third row such that the result in the third is modified. Also , observe that since A+M -> F and in the third A+M -> O , O = F + 1 (O must be A+M which is F plus a carry which in addition can't be greater than 1) in the second row where there is that M+I -> O there is no carry since that would imply also that M+I+1 = O therefore making M+I = M+A which is not possible. By knowing this we can find out the values for O and F such that they are consistent with the conditions found here. Since M+I -> O and F (that is A+M) + 1 -> O , F and O must be at a distance of 1 therefore there must be a sum of M+A which is smaller than 10 and a sum of M+I which is bigger than 10 such that the final resulting numbers (O and F) in their corresponding rows are consecutive which is possible just when O = 0 and F=9 since for setting any other value for one of them (say O) the corresponding value for the other wouldn't be at a distance of 1 as a result of the fact that when M+A < 10 and M+I > 10 for any M the last number of the sum M+A will be above M and in the second sum , M+I , it will be smaller their being the closest for the values of the minimum value in the first of M+1 and and the maximum in the second of M+9 , that is of M-1 therefore being at a minimum difference of 2. Therefore O = 0 and F=9. From here we can check cases such for the first rows there is one number (M) which added with two other gives 10 and 9 (A and I) and for the next 2 rows there is also another number (L) which added with two other different numbers (E and L) gives two other different numbers (P and R) though such an approach would be pretty annoying and I'm pretty convinced that a nicer way is.

Yup! Identifying that "distance between O and F is 1" is the crux in solving it. The others are just some trial and error.

Thanks for solving it! =D

Pi Han Goh - 5 years, 2 months ago

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Well , you're welcome! Anyways, I still think that if it is tried to look at the problem considering the way the numbers behave there can be some easier way. When I say that I am thinking at an understanding based on the way by which for choices of (M , (A,I)) would correspond the values of the other letters in such a way that would be consistent with the conditions imposed in the equation (that is L added with C and E gives P and R). This would be an understanding of the way structurally this numbers behave and would be an approach which wouldn't make necessary the trial and error thing which is nonetheless an useful way if you program things and have some organizing of the procedure to find such numbers anyways.

A A - 5 years, 2 months ago

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