document.write( "Question 1205180: What's the total of one, two, three-digit prime numbers that can be formed using the digits 2, 3, 5 and 7. No digit can be used more than once in a number. \n" ); document.write( "

Algebra.Com's Answer #841822 by math_tutor2020(3817) $\"\"$ $\"About$

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\n" ); document.write( "The numbers 2,3,5, and 7 are prime since the only factors are 1 and themselves.\r
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\n" ); document.write( "\n" ); document.write( "Make a 4x4 table listing the values 2,3,5,7 along the left and top like so
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	2	3	5	7
2
3
5
7

\n" ); document.write( "Cross out the northwest main diagonal. This is because we cannot re-use the same digit twice.
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	2	3	5	7
2	X
3		X
5			X
7				X

\n" ); document.write( "The remaining cells are filled in by concatenating the headers. I'll have the left header go first and then the top next.
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	2	3	5	7
2	X	23	25	27
3	32	X	35	37
5	52	53	X	57
7	72	73	75	X

\n" ); document.write( "The \"2\" column and \"5\" column can be crossed out because of the divisibility by 2 and divisibility by 5 rules.
\n" ); document.write( "27 is composite since 27 = 3*9
\n" ); document.write( "57 is composite since 57 = 3*19
\n" ); document.write( "Or you can use the divisibility by 3 rule to check 27 and 57 are multiples of 3.\r
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\n" ); document.write( "\n" ); document.write( "Of that table, the primes are: 23, 37, 53, 73
\n" ); document.write( "Refer to a list of primes. Or you can check each one by one. \r
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\n" ); document.write( "\n" ); document.write( "I'll let you handle the possible 3 digit primes that can be formed with 2,3,5,7.
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