A 3-digit number is the product of 4 prime numbers. Given that the 3 digits of the number are all prime & different and that the sum of ...its prime factors is 30, find the number.

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neela | High School Teacher | (Level 3) Valedictorian

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The prime digits are 2,3,5 and 7.

So we can form only 4! numbers which are different 3 digit prime numbers. So our choice number is from of these 24 numbers. In fact these could be physically tried. But a short cut is always better. So we proceed as shown below:

 Since the factors of the number are 4 prime numbers, which add up to 30, we should have the factors 2,3,5,7,11,13,17,19,23 and 29.

Examining the different primes from 2 to 29 , no 4 different primes add up to 30.

However , the conditions given say only different prime 3 digits. But the condition does not say the 4 factors should  be different primes.

If  the  3 digit prime number allows for 4 prime factors , not neccesarily different, then 2*2*7*19 = 532 is a solution.


Number of factors are four .

Factors are: 2, 2, 7 and 19.

All are prime factors.

Sum of the factors: 2+2+7+19 = 30.

The digits of 532 are  5, 3 and 2 are three  distinct primes.

Hope this helps.

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