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 Counting triplets III (Posted on 2011-11-14)
Consider three prime numbers A, B and C with A ≤ B ≤ C ≤ 20, and determine the total number of triplets (A, B, C) such that the respective last digits of A+B+C and A*B*C are the same. No computer programs!

 No Solution Yet Submitted by K Sengupta No Rating

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The primes classified by ending digit:

`1    112     23  3,135     57  7,179    19`

The combinations of ending digits that lead to a match between the sum and the product end digits, with the number of ways of getting that combination of ending digits.

`combination   quantity    sum/prod     123          2          6    137          4          1    159          1          5    233          3          8    235          2          0    237          4          2    239          2          4    337          6          3    357          4          5    377          6          7    379          4          9    555          1          5               ----      total     39`

 Posted by Charlie on 2011-11-14 16:07:47

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