abc ... not d?

a,b and c are single digit natural numbers. If

a a a a a a = b × c × b c × ( 2 c b ) × ( 2 b + c ) \overline { aaaaaa }=b\times c\times \overline { bc } \times (2c-b)\times (2b+c)
Find a × b × c a\times b\times c .

Details and Assumption x y z \overline { xyz } is a three digit number of the form 100 x + 10 y + z 100x+10y+z

This problem is a part of my set The Best of Me


The answer is 21.

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1 solution

Siddharth G
Jul 10, 2014

a a a a a a c a n b e w r i t t e n a s a ( 111111 ) \overline { aaaaaa } can\quad be\quad written\quad as\quad a(111111) . Factoring 111111 gives us
111111 = 3 × 7 × 11 × 13 × 37 111111=3\times 7\times 11\times 13\times 37 b × c × b c × ( 2 c b ) × ( 2 b + c ) h a s t h e f a c t o r s 3 , 7 , 11 , 13 , 37 b × c × ( 10 b + c ) × ( 2 c b ) × ( 2 b + c ) h a s t h e f a c t o r s 3 , 7 , 11 , 13 , 37 \Rightarrow b\times c\times \overline { bc } \times (2c-b)\times (2b+c)\quad has\quad the\quad factors\quad 3,7,11,13,37\\ \Rightarrow b\times c\times (10b+c)\times (2c-b)\times (2b+c)\quad has\quad the\quad factors\quad 3,7,11,13,37\\ \quad
Since b and c are single digit numbers, only 10b+c is a multiple of 37
10 b + c = 74 o r 37 I f 74 , t h e n , b = 7 , c = 4 b × c × ( 10 b + c ) × ( 2 c b ) × ( 2 b + c ) = 7 × 4 × 74 × 1 × 18 \Rightarrow 10b+c=74\quad or\quad 37 \quad \quad If\quad 74,then,\quad b=7,c=4\\ \Rightarrow b\times c\times (10b+c)\times (2c-b)\times (2b+c)=7\times 4\times 74\times 1\times 18


But nor 11 neither 13 are its factors. I f 37 , t h e n , b = 3 , c = 7 b × c × ( 10 b + c ) × ( 2 c b ) × ( 2 b + c ) = 3 × 7 × 37 × 11 × 13 = 111111 If\quad 37,\quad then,b=3,c=7\\ \Rightarrow b\times c\times (10b+c)\times (2c-b)\times (2b+c)=3\times 7\times 37\times 11\times 13=111111 Hence a=1, b=3, c=7. a b c = 21 \Rightarrow abc=\boxed { 21 }

really nice!

Adarsh Kumar - 6 years, 8 months ago

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