9999931996.9999933-5-5555571996.555557=......1....7-.....1.....7=....7-...7=...0 tan cung la 0 nen chia het cho5
9999931999=9999934k+3=9999934k.9999933=1.7=7(mod 10)
5555571997=5555574k+1=5555574k.555557=1.7=7(mod 10)
ta có : A=9999931997-5555571997=7-7=0(mod 10)
hay A chia hết cho 5