Răspuns :
324 + 563 + 5 x 6 x 7 x 8 x 9 - ( a x 120 + 3 ) =
324 + 563 + 30x7 x 8 x 9 - ( a x 120 + 3 ) =
324 + 563 + 210 x 8 x 9 - ( a x 120 + 3 ) =
324 + 563 + 1680 x 9 - ( a x 120 + 3 ) =
324 + 563 + 15120 - ( a x 120 + 3 ) =
16007 - ( a x 120 + 3)
deci ultima cifra a nr.16007=7
a*120=0
3=3
deci 7-(0+3)=7-3=4
324 + 563 + 30x7 x 8 x 9 - ( a x 120 + 3 ) =
324 + 563 + 210 x 8 x 9 - ( a x 120 + 3 ) =
324 + 563 + 1680 x 9 - ( a x 120 + 3 ) =
324 + 563 + 15120 - ( a x 120 + 3 ) =
16007 - ( a x 120 + 3)
deci ultima cifra a nr.16007=7
a*120=0
3=3
deci 7-(0+3)=7-3=4