Đáp án:
$10^{9}$ + $10^{8}$ + $10^{7}$
= $10^{7+2}$ + $10^{7+1}$ + $10^{7}$
= $10^{7}$ . $10^{2}$ + $10^{7}$ . 10 + $10^{7}$
= $10^{7}$ . 100 + $10^{7}$ . 10 + $10^{7}$
= $10^{7}$ . (100 + 10 + 1)
= $10^{7}$ . 111
Ta thấy: $10^{7}$ chia hết cho 5 => $10^{7}$ . 111 ⋮ 555.
=> ĐPCM
Chúc học tốt!!!