mk k viet dau gach tren dau ban tu viet nhe mk giai thui
abcde x 9 = edcba
=> a = 1 => e = 9
=>1bcd9 x 9 = 9dcb1
<=>( 10009 + 10bcd) x 9 =90001+ 10dcb
<=> 8 + 9bcd =dcb
b = 1
................... ban tu giai tiep
vay abcde = 10989
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