abc + def chia hết cho 37 ( theo đề bài ) => 1000 ( abc + def ) cũng chia hết 37

ta có : 1000 abc + 1000def <=> 1000abc + def + 999def

hay : abcdef + 999def ( chia hết cho 37 )

mà 999def chia hết cho 37 => abcdef cũng chia hết cho 37 => dpcm 

bang 15685

168 + 47 = 215

528 - 52 = 476

652 - 62 = 590

78 + 713 = 791

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Quãng đường kim giờ và kim phút đi được đến khi thỏa bài toán lần lượt là:

\(\hept{\begin{cases}S_h=v_h.t=t\\S_p=v_p.t=12t\end{cases}}\)

Mà ta có

\(S_p-S_h=9\Leftrightarrow12t-t=11t=9\)

\(\Rightarrow t=\frac{9}{11}\)